Magnetic tape, magnetic tape cartridge, and magnetic tape apparatus

ABSTRACT

The magnetic tape includes a non-magnetic support and a magnetic layer including ferromagnetic powder and a binding agent, in which the magnetic layer has a timing-based servo pattern, an edge shape of the timing-based servo pattern, specified by magnetic force microscopy is a shape in which a difference (L 99.9 −L 0.1 ) between a value L 99.9  of a cumulative distribution function of 99.9% and a value L 0.1  of a cumulative distribution function of 0.1% in a position deviation width from an ideal shape of the magnetic tape in a longitudinal direction is 180 nm or less, and an isoelectric point of a surface zeta potential of the magnetic layer is 3.8 or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2019-016523 filed on Jan. 31, 2019. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape, a magnetic tapecartridge, and a magnetic tape apparatus.

2. Description of the Related Art

A magnetic recording and reproducing apparatus which performs recordingof data on a magnetic recording medium and/or reading (reproducing) ofthe recorded data is widely divided into a magnetic disk apparatus and amagnetic tape apparatus. A representative example of the magnetic diskapparatus is a hard disk drive (HDD). In the magnetic disk apparatus, amagnetic disk is used as the magnetic recording medium. Meanwhile, inthe magnetic tape apparatus, a magnetic tape is used as the magneticrecording medium.

In both of the magnetic disk apparatus and the magnetic tape apparatus,it is preferable to narrow a recording track width, in order to increaserecording capacity (to make high capacity). On the other hand, as therecording track width is narrowed, a signal of an adjacent track iseasily mixed with a signal of a reading target track during thereproducing, and accordingly, it is difficult to maintain reproducingquality in a signal-to-noise ratio (SNR) or the like. In this regard, inrecent years, it is proposed to improve reproducing quality by reading asignal of a recording track by a plurality of reading elements (alsoreferred to as “reproducing elements”) two-dimensionally (for example,see JP2016-110680A, JP2011-134372A, and U.S. Pat. No. 7,755,863B). In acase where the reproducing quality can be improved by doing so, thereproducing quality can be maintained, even in a case where therecording track width is narrowed, and accordingly, it is possible toincrease recording capacity by narrowing the recording track width.

SUMMARY OF THE INVENTION

In JP2016-110680A and JP2011-134372A, studies regarding a magnetic diskapparatus are conducted. Meanwhile, in recent years, a magnetic tape isreceiving attention as a data storage medium for storing a large amountof data for a long period of time. However, the magnetic tape apparatusis generally a sliding type apparatus in which data reading(reproducing) is performed due to contact and sliding between themagnetic tape and a reading element. Accordingly, a relative positionbetween the reading element and a reading target track easily changesduring the reproducing, and the reproducing quality in the magnetic tapeapparatus tends to be hardly improved, compared to that in the magneticdisk apparatus. U.S. Pat. No. 7,755,863B discloses the descriptionregarding the magnetic tape apparatus (tape drive), but does notdisclose specific means for improving the reproducing quality of themagnetic tape apparatus.

An object of an aspect of the present invention is to provide a magnetictape capable of reproducing data with excellent reproducing quality in amagnetic tape apparatus that uses a plurality of reading elements(reproducing elements).

An aspect of the present invention relates to a magnetic tapecomprising: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binding agent, in which the magnetic layerhas a timing-based servo pattern, an edge shape of the timing-basedservo pattern, specified by magnetic force microscopy is a shape inwhich a difference L_(99.9)−L_(0.1) between a value L_(99.9) of acumulative distribution function of 99.9% and a value L_(0.1) of acumulative distribution function of 0.1% in a position deviation widthfrom an ideal shape of the magnetic tape in a longitudinal direction is180 nm or less, and an isoelectric point of a surface zeta potential ofthe magnetic layer is 3.8 or less.

In an aspect, the isoelectric point may be 2.5 or more and 3.8 or less.

In an aspect, the binding agent may be a binding agent containing anacidic group.

In an aspect, the acidic group may include at least one type of acidicgroup selected from the group consisting of a sulfonic acid group and asalt thereof.

In an aspect, the timing-based servo pattern may be a linear servopattern which continuously extends from one side of the magnetic tape ina width direction to the other side thereof and is inclined at an angleα with respect to the width direction, and the ideal shape may be alinear shape extending in a direction of the angle α.

In an aspect, the difference (L_(99.9)−L_(0.1)) may be 100 nm or moreand 180 nm or less.

In an aspect, the magnetic tape may further comprise a non-magneticlayer including non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer.

In an aspect, the magnetic tape may further comprise a back coatinglayer including non-magnetic powder and a binding agent on a surfaceside of the non-magnetic support opposite to a surface side providedwith the magnetic layer.

An aspect of the present invention relates to a magnetic tape cartridgecomprising the above magnetic tape.

An aspect of the present invention relates to a magnetic tape apparatuscomprising: the above described magnetic tape; a reading element unit;and an extraction unit, in which the reading element unit includes aplurality of reading elements each of which reads data from a specifictrack region including a reading target track in a track region includedin the magnetic tape, and the extraction unit performs a waveformequalization process with respect to each reading result for eachreading element, to extract, from the reading result, data derived fromthe reading target track.

In an aspect, each of the plurality of reading elements may read data bya linear scanning method from the specific track region including thereading target track in the track region included in the magnetic tape.

In an aspect, the waveform equalization process may be a waveformequalization process according to a deviation amount in position betweenthe magnetic tape and the reading element unit.

In an aspect, the waveform equalization process may be performed byusing a tap coefficient determined in accordance with the deviationamount.

In an aspect, the deviation amount may be determined in accordance witha result obtained by reading the timing-based servo pattern of themagnetic layer of the magnetic tape using a servo element.

In an aspect, the reading element unit may include a servo element and areading operation by the reading element unit may be performedsynchronously with a reading operation by the servo element.

In an aspect, parts of the plurality of reading elements may beoverlapped each other in a running direction of the magnetic tape.

In an aspect, the specific track region may be a region including thereading target track and an adjacent track which is adjacent to thereading target track, and each of the plurality of reading elements maystraddle over both of the reading target track and the adjacent track,in a case where a positional relationship with the magnetic tape ischanged.

In an aspect, the plurality of reading elements may be disposed in aline in a state of being adjacent to each other, in a width direction ofthe magnetic tape.

In an aspect, the plurality of reading elements may fall in the readingtarget track in a width direction of the magnetic tape.

In an aspect, regarding each of the plurality of reading elements, aratio between an overlapping region with the reading target track and anoverlapping region with an adjacent track which is adjacent to thereading target track may be specified from the deviation amount, and thetap coefficient may be determined in accordance with the specifiedratio.

In an aspect, the extraction unit may include a two-dimensional finiteimpulse response (FIR) filter, and the two-dimensional FIR filter maycompose each result obtained by performing the waveform equalizationprocess with respect to each reading result for each reading element, toextract, from the reading result, data derived from the reading targettrack.

In an aspect, the plurality of reading elements may be a pair of readingelements.

According to an aspect of the present invention, it is possible toprovide a magnetic tape with which a magnetic tape apparatus using aplurality of reading elements (reproducing elements) can reproduce datawith excellent reproducing quality. According to an aspect of thepresent invention, it is possible to provide a magnetic tape cartridgeincluding the magnetic tape. According to an aspect of the presentinvention, it is possible to provide a magnetic tape apparatus includingthe magnetic tape and a plurality of reading elements (reproducingelements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration view showing an example of an entireconfiguration of a magnetic tape apparatus.

FIG. 2 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading head and a magnetic tapeincluded in the magnetic tape apparatus.

FIG. 3 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a reading element unit and the magnetictape.

FIG. 4 is a schematic plan view showing an example of a schematicconfiguration in a plan view of a track region and a reading elementpair.

FIG. 5 is a graph showing an example of a correlation between an SNRregarding each of single reading element data and first composite dataunder a first condition, and track off-set.

FIG. 6 is a graph showing an example of a correlation between an SNRregarding each of single reading element data and second composite dataunder a second condition, and track off-set.

FIG. 7 is a block diagram showing an example of a main configuration ofhardware of an electric system of the magnetic tape apparatus.

FIG. 8 is a conceptual view provided for description of a method ofcalculating a deviation amount.

FIG. 9 is a flowchart showing an example of a flow of a magnetic tapereading process.

FIG. 10 is a conceptual view provided for description of a processperformed by a two-dimensional FIR filter of an extraction unit.

FIG. 11 is a schematic plan view showing an example of a state where thereading element unit straddles over a reading target track and a secondnoise mixing source track.

FIG. 12 is a schematic plan view showing a first modification example ofthe reading element unit.

FIG. 13 is a schematic plan view showing a second modification exampleof the reading element unit.

FIG. 14 shows a disposition example of a data band and a servo band.

FIG. 15 shows a disposition example of a servo pattern of alinear-tape-open (LTO) Ultrium format tape.

FIG. 16 is a view for describing an angle α regarding an edge shape ofthe servo pattern.

FIG. 17 is a view for describing an angle α regarding an edge shape ofthe servo pattern.

FIG. 18 shows an example of the edge shape of the servo pattern.

FIG. 19 shows an example of the servo pattern.

FIG. 20 shows an example of the servo pattern.

FIG. 21 shows an example of the servo pattern.

FIG. 22 is a conceptual view provided for description of a firstexample.

FIG. 23 is a conceptual view provided for description of a secondexample.

FIG. 24 is a view showing an example of a two-dimensional image of areproducing signal obtained from a single reading element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, first, a configuration of a magnetic tape apparatus using aplurality of reading elements (reproducing elements) will be described.

The magnetic tape apparatus includes a magnetic tape, a reading elementunit, and an extraction unit. With respect to reading data from themagnetic tape, in an example shown in FIG. 22, an elongated reading head200 comprises a plurality of reading elements 202 along a longitudinaldirection. In a magnetic tape 204, a plurality of tracks 206 are formed.The reading head 200 is disposed so that the longitudinal directioncoincides with a width direction of the magnetic tape 204. In addition,each of the plurality of reading elements 202 is allocated for each ofthe plurality of tracks 206 in a one-to-one relation, and reads datafrom the track 206 at a position faced.

However, in general, the magnetic tape 204 expands and contracts due totime elapse, an environment, a change of a tension, and the like. In acase where the magnetic tape expands and contracts in a width directionof the magnetic tape 204, the center of each of the reading elements 202disposed on both ends in the longitudinal direction in the reading head200 is deviated from the center of the track 206. In a case where themagnetic tape 204 is deformed due to the expansion and contraction in awidth direction, particularly, the reading elements 202 closer to bothends of the reading head 200, among the plurality of reading elements202, receive a greater effect of off-track. In order to reduce theeffect of the off-track, for example, a method of applying a surpluswidth to the width of the track 206 has been considered. However, as thewidth of the track 206 increases, a recording capacity of the magnetictape 204 decreases.

In addition, as shown in FIG. 23 as an example, in general, a servoelement 208 is provided in the reading head 200. Regarding a magnetictape 204, a servo pattern formed on a magnetic layer of the magnetictape 204 is read by the servo element 208. A control device (not shown)specifies that which position on the magnetic tape 204 the readingelement 202 runs on, for example, at regular time interval, from theservo signal obtained by reading the servo pattern by the servo element208. Accordingly, a position error signal (PES) in a width direction ofthe magnetic tape 204 is detected by the control device.

As described above, in a case where the control device specifies arunning position of the reading element 202, a feedback control isperformed with respect to an actuator (not shown) for the reading headby the control device based on the specified running position, andaccordingly, tracking by the magnetic tape 204 in the width direction isrealized.

However, although the tracking is performed, sharp vibration, ahigh-frequency component of jitter, and the like are factors of anincrease in PES, and this causes a deterioration in reproducing qualityof data read from a reading target track.

On the other hand, in a case where data is each read by the plurality ofreading elements from a specific track region including a reading targettrack in a track region included in the magnetic tape, a waveformequalization process is performed with respect to each reading resultfor each reading element, and data derived from the reading target trackis extracted from the reading result, it is possible to improvereproducing quality of the data read from the reading target track,compared to a case where data is read by only a single reading elementfrom the reading target track. As a result, it is possible to increasean acceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality.

Here, in a case where a change of the relative position between thereading element and the reading target track (hereinafter, referred toas “relative positional change”) is large, a waveform equalizationprocess performed on each of the reading results for each of theplurality of reading elements may not necessarily be a most suitablewaveform equalization process for each read result. For example, awaveform equalization process performed by a two-dimensional FIR filtermay not necessarily be a most suitable waveform equalization process foreach reading result. On the other hand, in a case where the relativepositional change can be suppressed, a more suitable waveformequalization process can be performed for each of the reading resultsread by the plurality of reading elements. As a result, it is possibleto increase an acceptable amount of a deviation amount, for ensuringexcellent reproducing quality with respect to data derived from thereading target track, extracted by performing the waveform equalizationprocess. In this regard, in the magnetic tape according to an aspect ofthe present invention, it is considered that the isoelectric point of asurface zeta potential of the magnetic layer of 3.8 or less leads tostabilization of a contact state between the magnetic tape and thereading element. It is supposed that this aspect contributes tosuppression of the relative positional change. This point will befurther described later.

Further, as the servo pattern is formed to be closer to a design shape(for example, ideal shape, details of which will be described later), anaccuracy of specifying the position where the reading element istraveling is higher. This also leads to an increase in an acceptableamount of a deviation amount (a track off-set amount), for ensuringexcellent reproducing quality. In this regard, the difference(L_(99.9)−L_(0.1)) is an index related to a shape of the servo pattern(timing-based servo pattern). Details thereof will be described later.

As described above, an increase in an acceptable amount of a deviationamount, for ensuring excellent reproducing quality can contribute to thereproducing with excellent reproducing quality (for example, high SNR orlow error rate), even in a case where a track margin (recording trackwidth-reproducing element width) is decreased. A decrease in a trackmargin can contribute to an increase in the number of recording trackscapable of being disposed in a width direction of the magnetic tape bydecreasing the recording track width, that is, realization of highcapacity.

Hereinafter, a magnetic tape, a magnetic tape cartridge, and a magnetictape apparatus according to an aspect of the present invention will bedescribed in more detail. In the following, the magnetic tape apparatusand the like may be described with reference to the drawings. However,the present invention is not limited to aspects shown in the drawings.

Configuration of Magnetic Tape Apparatus and Magnetic Tape ReadingProcess

As shown in FIG. 1 as an example, a magnetic tape apparatus 10 comprisesa magnetic tape cartridge 12, a transportation device 14, a reading head16, and a control device 18.

The magnetic tape apparatus 10 is an apparatus which extracts a magnetictape MT from the magnetic tape cartridge 12 and reads data from theextracted magnetic tape MT by using the reading head 16 by a linearscanning method. The reading of data can also be referred to asreproducing of data.

The control device 18 controls the entire magnetic tape apparatus 10. Inan aspect, the control performed by the control device 18 can berealized with an application specific integrated circuit (ASIC). Inaddition, in an aspect, the control performed by the control device 18can be realized with a field-programmable gate array (FPGA). The controlperformed by the control device 18 may be realized with a computerincluding a central processing unit (CPU), a read only memory (ROM), anda random access memory (RAM). Further, the control may be realized witha combination of two or more of AISC, FPGA, and the computer.

The transportation device 14 is a device which selectively transportsthe magnetic tape MT in a forward direction and a backward direction,and comprises a sending motor 20, a winding reel 22, a winding motor 24,a plurality of guide rollers GR, and the control device 18.

A cartridge reel CR is provided in the magnetic tape cartridge 12. Themagnetic tape MT is wound around the cartridge reel CR. The sendingmotor 20 causes the cartridge reel CR in the magnetic tape cartridge 12to be rotatably driven under the control of the control device 18. Thecontrol device 18 controls the sending motor 20 to control a rotationdirection, a rotation rate, a rotation torque, and the like of thecartridge reel CR.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the sending motor 20 so that the magnetictape MT runs in a forward direction. A rotation rate, a rotation torque,and the like of the sending motor 20 are adjusted in accordance with aspeed of the magnetic tape MT wound around the winding reel 22.

The winding motor 24 causes the winding reel 22 to be rotatably drivenunder the control of the control device 18. The control device 18controls the winding motor 24 to control a rotation direction, arotation rate, a rotation torque, and the like of the winding reel 22.

In a case of winding the magnetic tape MT around the winding reel 22,the control device 18 rotates the winding motor 24 so that the magnetictape MT runs in the forward direction. A rotation rate, a rotationtorque, and the like of the winding motor 24 are adjusted in accordancewith a speed of the magnetic tape MT wound around the winding reel 22.

By adjusting the rotation rate, the rotation torque, and the like ofeach of the sending motor 20 and the winding motor 24 as describedabove, a tension in a predetermined range is applied to the magnetictape MT. Here, the predetermined range indicates a range of a tensionobtained from a computer simulation and/or a test performed with a realmachine, as a range of a tension at which data can be read from themagnetic tape MT by the reading head 16, for example.

In a case of rewinding the magnetic tape MT to the cartridge reel CR,the control device 18 rotates the sending motor 20 and the winding motor24 so that the magnetic tape MT runs in the backward direction.

In an aspect, the tension of the magnetic tape MT is controlled bycontrolling the rotation rate, the rotation torque, and the like of eachof the sending motor 20 and the winding motor 24. In addition, in anaspect, the tension of the magnetic tape MT may be controlled by using adancer roller, or may be controlled by drawing the magnetic tape MT to avacuum chamber.

Each of the plurality of guide rollers GR is a roller guiding themagnetic tape MT. A running path of the magnetic tape MT is determinedby separately disposing the plurality of guide rollers GR on positionsstraddling over the reading head 16 between the magnetic tape cartridge12 and the winding reel 22.

The reading head 16 comprises a reading unit 26 and a holder 28. Thereading unit 26 is held by the holder 28 so as to come into contact withthe magnetic tape MT during running.

As shown in FIG. 2 as an example, the magnetic tape MT comprises a trackregion 30 and a servo pattern 32. The servo pattern 32 is a pattern usedfor detection of the position of the reading head 16 on the magnetictape MT. The servo pattern 32 is a pattern in which a first diagonalline 32A at a first predetermined angle (for example, 95 degrees) and asecond diagonal line 32B at a second predetermined angle (for example,85 degrees) are alternately disposed on both end portions in a tapewidth direction at a constant pitch (cycle) along a running direction ofthe magnetic tape MT. The “tape width direction” here indicates a widthdirection of the magnetic tape MT.

The track region 30 is a region where data which is a reading target iswritten, and is formed on the center of the magnetic tape MT in the tapewidth direction. The “center in the tape width direction” hereindicates, for example, a region between the servo pattern 32 on one endportion and the servo pattern 32 on the other end portion of themagnetic tape MT in the tape width direction. Hereinafter, forconvenience of description, the “running direction of the magnetic tapeMT” is simply referred to as the “running direction”.

The reading unit 26 comprises a servo element pair 36 and a plurality ofreading element units 38. The holder 28 is formed to be elongated in thetape width direction, and a total length of the holder 28 in thelongitudinal direction is longer than the width of the magnetic tape MT.The servo element pair 36 is disposed on both end portions of the holder28 in the longitudinal direction, respectively, and the plurality ofreading element units 38 are disposed on the center of the holder 28 inthe longitudinal direction.

The servo element pair 36 comprises servo elements 36A and 36B. Theservo element 36A is disposed on a position facing the servo pattern 32on one end portion of the magnetic tape MT in the tape width direction,and the servo element 36B is disposed on a position facing the servopattern 32 on the other end portion of the magnetic tape MT in the tapewidth direction.

In the holder 28, the plurality of reading element units 38 are disposedbetween the servo element 36A and the servo element 36B along the tapewidth direction. The track region 30 comprises the plurality of tracksat regular interval in the tape width direction, and in a default stateof the magnetic tape apparatus 10, each of the plurality of readingelement units 38 is disposed to face each track in the track region 30.

Accordingly, the reading unit 26 and the magnetic tape MT relativelymove linearly along the longitudinal direction of the magnetic tape MT,and thus, data of each track in the track region 30 is read by eachreading element unit 38 at the corresponding position among theplurality of reading element units 38 by the linear scanning method. Inaddition, in the linear scanning method, the servo patterns 32 are readby the servo element pair 36 synchronously with the reading operation ofthe reading element units 38. That is, in an aspect of the linearscanning method, the reading with respect to the magnetic tape MT isperformed in parallel by the plurality of reading element units 38 andthe servo element pair 36.

Here, “each track in the track region 30” described above indicates atrack included in “each of a plurality of specific track regions eachincluding the reading target track in the track region included in themagnetic tape”.

The “default state of the magnetic tape apparatus 10” indicates a statewhere the magnetic tape MT is not deformed and a positional relationshipbetween the magnetic tape MT head the reading head 16 is a correctpositional relationship. Here, the “correct positional relationship”indicates, for example, a positional relationship in which the center ofthe magnetic tape MT in the tape width direction and the center of thereading head 16 in the longitudinal direction coincide with each other.

In an aspect, each of the plurality of reading element unit 38 has thesame configuration. Hereinafter, the description will be performed usingone of the plurality of reading element unit 38 as an example, forconvenience of description. As shown in FIG. 3 as an example, thereading element unit 38 comprises a pair of reading elements. In theexample shown in FIG. 3, “a pair of reading elements” indicates a firstreading element 40 and a second reading element 42. Each of the firstreading element 40 and the second reading element 42 reads data from aspecific track region 31 including a reading target track 30A in thetrack region 30.

In the example shown in FIG. 3, for convenience of description, onespecific track region 31 is shown. In practice, in general, in the trackregion 30, a plurality of the specific track regions 31 are present, andthe reading target track 30A is included in each specific track region31. The reading element unit 38 is allocated to each of the plurality ofspecific track regions 31 in a one-to-one manner. Specifically, thereading element unit 38 is allocated to the reading target track 30A ineach of the plurality of specific track regions 31 in a one-to-onemanner.

The specific track region 31 indicates three adjacent tracks. A firsttrack among the three adjacent tracks is the reading target track 30A inthe track region 30. A second track among the three adjacent tracks is afirst noise mixing source track 30B which is one adjacent track adjacentto the reading target track 30A. A third track among the three adjacenttracks is a second noise mixing source track 30C which is one adjacenttrack adjacent to the reading target track 30A. The reading target track30A is a track at a position facing the reading element unit 38 in thetrack region 30. That is, the reading target track 30A indicates a trackhaving data to be read by the reading element unit 38.

The first noise mixing source track 30B is a track which is adjacent tothe reading target track 30A on one side in the tape width direction andis a mixing source of noise mixed to data read from the reading targettrack 30A. The second noise mixing source track 30C is a track which isadjacent to the reading target track 30A on the other side in the tapewidth direction and is a mixing source of noise mixed to data read fromthe reading target track 30A. Hereinafter, for convenience ofdescription, in a case where it is not necessary to describe the firstnoise mixing source track 30B and the second noise mixing source track30C separately, these are referred to as the “adjacent track” withoutreference numerals.

In an aspect, in the track region 30, the plurality of specific trackregions 31 are disposed at regular interval in the tape width direction.For example, in the track region 30, 32 specific track regions 31 aredisposed at regular interval in the tape width direction, and thereading element unit 38 is allocated to each specific track region 31 ina one-to-one manner.

The first reading element 40 and the second reading element 42 aredisposed at positions parts of which are overlapped in the runningdirection, in a state of being adjacent in the running direction. In adefault state of the magnetic tape apparatus 10, the first readingelement 40 is disposed at a position straddling over the reading targettrack 30A and the first noise mixing source track 30B. In a defaultstate of the magnetic tape apparatus 10, the second reading element 42is disposed at a position straddling over the reading target track 30Aand the first noise mixing source track 30B.

In a default state of the magnetic tape apparatus 10, an area of aportion of the first reading element 40 facing the reading target track30A is greater than an area of a portion of the first reading element 40facing the first noise mixing source track 30B, in a plan view.Meanwhile, in a default state of the magnetic tape apparatus 10, an areaof a portion of the second reading element 42 facing the first noisemixing source track 30B is greater than the area of a portion of thefirst reading element 40 facing the reading target track 30A, in a planview.

The data read by the first reading element 40 is subjected to a waveformequalization process by a first equalizer 70 (see FIG. 7) which will bedescribed later. The data read by the second reading element 42 issubjected to a waveform equalization process by a second equalizer 72(see FIG. 7) which will be described later. Each data obtained byperforming the waveform equalization process by each of the firstequalizer 70 and the second equalizer 72 is added by an adder 44 andcomposed.

In FIG. 3, the aspect in which the reading element unit 38 includes thefirst reading element 40 and the second reading element 42 has beendescribed as an example. Here, for example, even in a case where onlyone reading element (hereinafter, also referred to as a single readingelement) among a pair of reading elements is used, a signalcorresponding to a reproducing signal obtained from the reading elementunit 38 is obtained.

In this case, for example, as shown in FIG. 8 as an example, thereproducing signal obtained from the single reading element is allocatedto a plane position on a track calculated from a servo signal obtainedby the servo element pair 36 synchronously with the reproducing signal.By repeating this operation while moving the single reading element inthe tape width direction, a two-dimensional image of the reproducingsignal (hereinafter, simply referred to as a “two-dimensional image”) isobtained. Here, a reproducing signal configuring the two-dimensionalimage or a part of the two-dimensional image (for example, a reproducingsignal corresponding to the positions of the plurality of tracks) is asignal corresponding to the reproducing signal obtained from the readingelement unit 38.

FIG. 24 shows an example of a two-dimensional image of the reproducingsignal obtained by using a loop tester, in the magnetic tape MT in aloop shape (hereinafter, also referred to as a “loop tape”). Here, theloop tester indicates a device which transports the loop tape in a statewhere the loop tape is repeatedly in contact with the single readingelement, for example. In order to obtain a two-dimensional image in thesame manner as in the case of the loop tester, a reel tester may be usedor an actual tape drive may be used. The “reel tester” here indicates adevice which transports the magnetic tape MT in a reel state, forexample.

As described above, even in a case where a head for a magnetic tapewhich does not include the reading element unit on which the pluralityof reading elements are loaded at adjacent positions is used, the effectaccording to the technique disclosed in this specification can bequantitatively evaluated. As an example of an index for quantitativelyevaluating the effect according to the technique disclosed in thisspecification, an SNR, an error rate, and the like are used.

FIGS. 4 to 6 show results obtained from experiments performed by thepresent inventors. As shown in FIG. 4 as an example, a reading elementpair 50 are disposed on a track region 49. The track region 49 includesa first track 49A, a second track 49B, and a third track 49C which areadjacent to one another in the tape width direction. The reading elementpair 50 includes a first reading element 50A and a second readingelement 50B. The first reading element 50A and the second readingelement 50B are disposed at positions adjacent to each other in the tapewidth direction. The first reading element 50A is disposed so as to facethe second track 49B which is the reading target track and fall in thesecond track 49B. In addition, the second reading element 50B isdisposed so as to face the first track 49A adjacent to one side of thesecond track 49B and fall in the first track 49A.

FIG. 5 shows an example of a correlation between an SNR regarding eachof single reading element data and first composite data under a firstcondition, and track off-set. In addition, FIG. 6 shows an example of acorrelation between an SNR regarding each of single reading element dataand second composite data under a second condition, and track off-set.

Here, the single reading element data indicates data obtained byperforming a waveform equalization process with respect to data read bythe first reading element 50A, in the same manner as in the case of thefirst reading element 40 shown in FIG. 3. The first condition indicatesa condition in which a reading element pitch is 700 nm (nanometers). Thesecond condition indicates a condition in which a reading element pitchis 500 nm. The reading element pitch indicates a pitch between the firstreading element 50A and the second reading element 50B in the tape widthdirection, as shown in FIG. 4 as an example. The track off-set indicatesa deviation amount between the center of the second track 49B in thetape width direction and the center of the first reading element 50A inthe track width direction, as shown in FIG. 4 as an example.

The first composite data indicates data composed by adding firstwaveform equalized data and second waveform equalized data obtainedunder the first condition. The first waveform equalized data indicatesdata obtained by performing the waveform equalization process withrespect to the data read by the first reading element 50A, in the samemanner as in the case of the first reading element 40 shown in FIG. 3.The second waveform equalized data indicates data obtained by performingthe waveform equalization process with respect to the data read by thesecond reading element 50B, in the same manner as in the case of thesecond reading element 42 shown in FIG. 3. The second composite dataindicates data composed by adding first waveform equalized data andsecond waveform equalized data obtained under the second condition.

In a case of comparing the SNR of the first composite data shown in FIG.5 to the SNR of the second composite data shown in FIG. 6, the SNR ofthe first composite data rapidly declines to generate a groove of thegraph in a range of the track off-set of −0.4 μm (micrometers) to 0.2μm, whereas the SNR of the second composite data does not rapidlydecline as the graph of the SNR of the first composite data. Each of theSNR of the first composite data and the SNR of the second composite datais higher than the SNR of the single reading element data, andparticularly, the SNR of the second composite data is higher than theSNR of the single reading element data over the entire range of thetrack off-set.

From the experimental results shown in FIGS. 5 and 6, the presentinventors have found that it is preferable to perform the reading ofdata in a state where the first reading element 50A and the secondreading element 50B are adjacent to each other in the tape widthdirection, compared to a case where the reading of data is performed byonly the first reading element 50A. The “state adjacent to each other”here means, for example, that the first reading element 50A and thesecond reading element 50B are not in contact with each other, but aredisposed in a line in the tape width direction, so that the SNR of thecomposite data becomes higher than the SNR of the single reading elementdata, over the entire range of the track off-set.

In an aspect, as shown in FIG. 3 as an example, in the reading elementunit 38, parts of the first reading element 40 and the second readingelement 42 are overlapped each other in the running direction, andaccordingly, a high density of the tracks included in the magnetic tapeMT is realized.

As shown in FIG. 7 as an example, the magnetic tape apparatus 10comprises an actuator 60, an extraction unit 62, analog/digital (A/D)converters 64, 66, and 68, a decoding unit 69, and a computer 73.

The control device 18 is connected to the servo element pair 36 throughthe analog/digital (A/D) converter 68. The A/D converter 68 outputs aservo signal obtained by converting an analog signal obtained by readingthe servo pattern 32 by the servo elements 36A and 36B included in theservo element pairs 36 into a digital signal, to the control device 18.

The control device 18 is connected to the actuator 60. The actuator 60is attached to the reading head 16 and applies power to the reading head16 under the control of the control device 18, to change the position ofthe reading head 16 in the tape width direction. The actuator 60includes, for example, a voice coil motor, and the power applied to thereading head 16 is power obtained by converting an electric energy basedon a current flowing through the coil into a kinetic energy, using anenergy of a magnet as a medium.

Here, the aspect in which the voice coil motor is loaded on the actuator60 has been described. Here, the magnetic tape apparatus is not limitedto the aspect, and for example, a piezoelectric element can also beused, instead of the voice coil motor. In addition, the voice coil motorand the piezoelectric element can be combined with each other.

In an aspect, the deviation amount of the positions of the magnetic tapeMT and the reading element unit 38 is determined in accordance with aservo signal which is a result obtained by reading the servo pattern 32by the servo element pair 36. The control device 18 controls theactuator 60 to apply power according to the deviation amount of thepositions of the magnetic tape MT and the reading element unit 38 to thereading head 16. Accordingly, the position of the reading head 16 ischanged in the tape width direction and the position of the reading head16 is adjusted to a normal position. Here, as shown in FIG. 3, thenormal position indicates, for example, a position of the reading head16 in a default state of the magnetic tape apparatus 10.

Here, the aspect in which the deviation amount of the positions of themagnetic tape MT and the reading element unit 38 is determined inaccordance with the servo signal which is the result obtained by readingthe servo pattern 32 by the servo element pair 36 is used as an example.However, the magnetic tape apparatus according to an aspect of thepresent invention is not limited to such an example. For example, as thedeviation amount of the positions of the magnetic tape MT and thereading element unit 38, the deviation amount from predeterminedreference positions of the servo element 36A and the magnetic tape MTmay be used, or the deviation amount of an end surface of the readinghead 16 and a center position of a specific track included in themagnetic tape MT may be used. As described above, the deviation amountof the positions of the magnetic tape MT and the reading element unit 38may be the deviation amount corresponding to the deviation amountbetween the center of the reading target track 30A in the tape widthdirection and the center of the reading head 16 in the tape widthdirection. Hereinafter, for convenience of description, the deviationamount of the positions of the magnetic tape MT and the reading elementunit 38 is simply referred to as a “deviation amount”.

For example, as shown in FIG. 8, the deviation amount is calculatedbased on a ratio of a distance A to a distance B. The distance Aindicates a distance calculated from a result obtained by reading thefirst diagonal line 32A and the second diagonal line 32B adjacent toeach other by the servo element 36A. The distance B indicates a distancecalculated from a result obtained by reading the two first diagonallines 32A adjacent to each other by the servo element 36A.

The extraction unit 62 comprises the control device 18 and atwo-dimensional FIR filter 71. The two-dimensional FIR filter 71comprises the adder 44, the first equalizer 70, and the second equalizer72.

The first equalizer 70 is connected to the first reading element 40through the A/D converter 64. In addition, the first equalizer 70 isconnected to each of the control device 18 and the adder 44. The dataread by the first reading element 40 from the specific track region 31is an analog signal, and the A/D converter 64 outputs a first readingsignal obtained by converting the data read by the first reading element40 from the specific track region 31 into a digital signal, to the firstequalizer 70.

The second equalizer 72 is connected to the second reading element 42through the A/D converter 66. In addition, the second equalizer 72 isconnected to each of the control device 18 and the adder 44. The dataread by the second reading element 42 from the specific track region 31is an analog signal, and the A/D converter 66 outputs a second readingsignal obtained by converting the data read by the second readingelement 42 from the specific track region 31 into a digital signal, tothe second equalizer 72. Each of the first reading signal and the secondreading signal is an example of a “reading result for each readingelement”.

The first equalizer 70 performs a waveform equalization process withrespect to the input first reading signal. For example, the firstequalizer 70 performs a convolution arithmetic operation of a tapcoefficient with respect to the input first reading signal, and outputsthe first arithmetic operation processed signal which is a signal afterthe arithmetic operation.

The second equalizer 72 performs a waveform equalization process withrespect to the input second reading signal. For example, the secondequalizer 72 performs a convolution arithmetic operation of a tapcoefficient with respect to the input second reading signal, and outputsthe second arithmetic operation processed signal which is a signal afterthe arithmetic operation.

Each of the first equalizer 70 and the second equalizer 72 outputs thefirst arithmetic operation processed signal and the second arithmeticoperation processed signal to the adder 44. The adder 44 adds andcomposes the first arithmetic operation processed signal input from thefirst equalizer 70 and the second arithmetic operation processed signalinput from the second equalizer 72, and outputs the composite dataobtained by the composite to the decoding unit 69.

Each of the first equalizer 70 and the second equalizer 72 is aone-dimensional FIR filter.

In an aspect, the FIR filter is a series of actual values includingpositive and negative values, the number of lines of the series isreferred to as a tap number, and the numerical value is referred to as atap coefficient. In addition, in an aspect, the waveform equalizationindicates a process of the convolution arithmetic operation(multiplication and accumulation) of the series of actual values, thatis, the tap coefficient, with respect to the reading signal. The“reading signal” here indicates a collective term of the first readingsignal and the second reading signal. In an aspect, the equalizerindicates a circuit which carries out a process of performing theconvolution arithmetic operation of the tap coefficient with respect tothe reading signal or the other input signal and outputting the signalafter the arithmetic operation. In addition, in an aspect, the adderindicates a circuit which simply adds two series. Weighting of the twoseries is reflected on the numerical values, that is, the tapcoefficient of the FIR filter used in the first equalizer 70 and thesecond equalizer 72.

The control device 18 performs the waveform equalization processaccording to the deviation amount with respect to each of the firstequalizer 70 and the second equalizer 72 by setting the tap coefficientaccording to the deviation amount with respect to the FIR filter of eachof the first equalizer 70 and the second equalizer 72.

The control device 18 comprises an association table 18A. Theassociation table 18A associates the tap coefficient with the deviationamount regarding each of the first equalizer 70 and the second equalizer72. A combination of the tap coefficient and the deviation amount is,for example, a combination obtained in advance as a combination of thetap coefficient and the deviation amount, with which the best compositedata is obtained by the adder 44, based on the result obtained byperforming at least one of the test performed with a real machine or asimulation. The “best composite data” here indicates data correspondingto the reading target track data.

Here, the “reading target track data” indicates “data derived from thereading target track 30A”. The “data derived from the reading targettrack 30A” indicates data corresponding to data written on the readingtarget track 30A. As an example of data corresponding to the datawritten on the reading target track 30A, data which is read from thereading target track 30A and to which a noise component from theadjacent tracks is not mixed is used.

As described above, the association table 18A is used as an example. Inanother aspect, an arithmetic expression may be used instead of theassociation table 18A. The “arithmetic expression” here indicates anarithmetic expression in which an independent variable is set as thedeviation amount and a dependent variable is set as the tap coefficient,for example.

As described above, the aspect in which the tap coefficient is derivedfrom the association table 18A, in which combinations of the tapcoefficients and the deviation amounts are regulated, has beendescribed. In another aspect, for example, the tap coefficient may bederived from the association table in which the combinations of tapcoefficients and ratios are regulated, or the arithmetic expression. The“ratio” here indicates a ratio between an overlapping region with thereading target track 30A and an overlapping region with the adjacenttrack, regarding each of the first reading element 40 and the secondreading element 42. The ratio is calculated and specified from thedeviation amount by the control device 18 and the tap coefficient isdetermined in accordance with the specified ratio. Alternatively, in anaspect, it is possible to determine a series of a series of a pluralityof the tap coefficients so as to minimize an error from a referencewaveform (target) which is an equalization target using a plurality ofthe reading results obtained by reading data by each of the plurality ofreading elements in a calibration region in advance, for example.

The decoding unit 69 decodes the composite data input from the adder 44and outputs a decoded signal obtained by the decoding to the computer73. The computer 73 performs various processes with respect to thedecoded signal input from the decoding unit 69.

Next, a magnetic tape reading process carried out by the extraction unit62 will be described with reference to FIG. 9. Hereinafter, forconvenience of description, the embodiment is described based onassumption that the servo signal is input to the control device 18, in acase where a period of sampling comes. Here, the sampling is not limitedto the sampling of the servo signal and also means the sampling of thereading signal. That is, in an aspect, the track region 30 is formed inparallel with the servo pattern 32 along the running direction, andaccordingly, the reading operation by the reading element unit 38 isperformed synchronously with the reading operation by the servo elementpair 36.

In the process shown in FIG. 9, first, in a step S100, the controldevice 18 determines whether or not the period of the sampling comes. Inthe step S100, in a case where the period of the sampling comes, thedetermination is affirmative and the magnetic tape reading process movesto a step S102. In the step S100, in a case where the period of thesampling does not come, the determination is denied, and thedetermination of the step S100 is performed again.

In a step S102, the first equalizer 70 acquires a first reading signal,the second equalizer 72 acquires a second reading signal, and then, themagnetic tape reading process moves to a step S104.

In the step S104, the control device 18 acquires a servo signal andcalculates a deviation amount from the acquired servo signal, and thenthe magnetic tape reading process moves to a step S106.

In the step S106, the control device 18 derives a tap coefficientcorresponding to the deviation amount calculated in the process of thestep S104 from the association table 18A, regarding first to third tapsof each of the first equalizer 70 and the second equalizer 72. That is,by performing the process of the step S106, an optimal combination isdetermined as a combination of a one-dimensional FIR filter which is anexample of the first equalizer 70 and a one-dimensional filter which isan example of the second equalizer 72. The “optimal combination” hereindicates, for example, a combination in which the composite data outputby performing a process of a step S112 which will be described later isset as data corresponding to the reading target track data.

In the next step S108, the control device 18 sets the tap coefficientderived in the process of the step S106 with respect to each of thefirst equalizer 70 and the second equalizer 72, and then the magnetictape reading process moves to a step S110.

In the step S110, the first equalizer 70 performs the waveformequalization process with respect to the first reading signal acquiredin the process of the step S102, and accordingly, the first arithmeticoperation processed signal is generated. The first equalizer 70 outputsthe generated first arithmetic operation processed signal to the adder44. The second equalizer 72 performs the waveform equalization processwith respect to the second reading signal acquired in the process of thestep S102, and accordingly, the second arithmetic operation processedsignal is generated. The second equalizer 72 outputs the generatedsecond arithmetic operation processed signal to the adder 44.

In the next step S112, the adder 44 adds and composes the firstarithmetic operation processed signal input from the first equalizer 70and the second arithmetic operation processed signal input from thesecond equalizer 72, as shown in FIG. 10 as an example. The adder 44outputs the composite data obtained by the composite to the decodingunit 69.

In a case where the reading element unit 38 is disposed in the specifictrack region 31, as the example shown in FIG. 3, the data correspondingto the reading target track data, from which the noise component fromthe first noise mixing source track 30B is removed, is output as thecomposite data, by performing the process of the step S112. That is, byperforming the processes of the step S102 to the step S112, theextraction unit 62 extracts only the data derived from the readingtarget track 30A.

In a case where the magnetic tape MT expands and contracts in the tapewidth direction or vibration is applied to at least one of the magnetictape MT or the reading head 16, the reading element unit 38 is displacedto a position shown in FIG. 11 from the position shown in FIG. 3 as anexample. In the example shown in FIG. 11, the first reading element 40and the second reading element 42 are disposed at positions straddlingover both of the reading target track 30A and the second noise mixingsource track 30C. In this case, by performing the processes of the stepS102 to the step S112, the data corresponding to the reading targettrack data, from which the noise component from the second noise mixingsource track 30C is removed, is output to the decoding unit 69 as thecomposite data.

In the next step S114, the control device 18 determines whether or not acondition for completing the magnetic tape reading process (hereinafter,referred to as a “completion condition”) is satisfied. The completioncondition indicates, for example, a condition in which the entiremagnetic tape MT is wound around the winding reel 22, a condition inwhich an instruction for forced completion of the magnetic tape readingprocess is applied from the outside, and the like.

In the step S114, in a case where the completion condition is notsatisfied, the determination is denied, and the magnetic tape readingprocess is moved to the step S100. In the step S114, in a case where thecompletion condition is satisfied, the determination is affirmative, andthe magnetic tape reading process ends.

As described above, in an aspect of the magnetic tape apparatus 10, thedata is read from the specific track region 31 by each of the firstreading element 40 and the second reading element 42 disposed in a stateof being adjacent to each other. In addition, the extraction unit 62performs the waveform equalization process according to the deviationamount with respect to each of the first reading element 40 and thesecond reading element 42, to extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal. Therefore, in the magnetic tape apparatus 10, it is possible toprevent a deterioration in reproducing quality of data read from thereading target track 30A by the linear scanning method, compared to acase where the data is read from the reading target track 30A by only asingle reading element by the linear scanning method.

In an aspect of the magnetic tape apparatus 10, parts of the firstreading element 40 and the second reading element 42 are overlapped eachother in the running direction. Therefore, in the magnetic tapeapparatus 10, it is possible to increase reproducing quality of dataread from the reading target track 30A by the linear scanning method,compared to a case where the entire portions of the plurality of readingelements are overlapped in the running direction.

In an aspect of the magnetic tape apparatus 10, the specific trackregion 31 includes the reading target track 30A, the first noise mixingsource track 30B, and the second noise mixing source track 30C, and eachof the first reading element 40 and the second reading element 42straddles over both of the reading target track 30A and the adjacenttrack, in a case where a positional relationship with the magnetic tapeMT is changed. Therefore, in the magnetic tape apparatus 10, it ispossible to reduce the noise component generated in one of the readingelement of the first reading element 40 and the second reading element42 due to entering the adjacent track from the reading target track 30Ain the tape width direction, by using the reading result obtained by theother reading element entering the adjacent track from the readingtarget track 30A in the tape width direction, compared to a case wherethe data is read by only the single reading element from the readingtarget track 30A.

In an aspect of the magnetic tape apparatus 10, the tap coefficient usedin the waveform equalization process is determined in accordance withthe deviation amount. Therefore, by determining the tap coefficient inaccordance with the deviation amount, it is possible to instantaneouslyreduce the noise component generated due to entering the reading targettrack 30A from the adjacent track in the tape width direction, inaccordance with a change of the positional relationship between themagnetic tape MT and the reading element unit 38, compared to a casewhere the tap coefficient is determined in accordance with a parameterwith no relation with the deviation amount.

In an aspect of the magnetic tape apparatus 10, regarding each of thefirst reading element 40 and the second reading element 42, the ratiobetween the overlapping region with the reading target track 30A and theoverlapping region with the adjacent track is specified from thedeviation amount, and the tap coefficient is determined according to thespecified ratio. Therefore, in the magnetic tape apparatus 10, it ispossible to exactly reduce the noise component, even in a case where thepositional relationship between the magnetic tape MT and the readingelement unit 38 is changed, compared to a case where the tap coefficientis determined in accordance with a parameter with no relation with aratio between the overlapping region with the reading target track 30Aand the overlapping region with the adjacent track regarding each of theplurality of reading elements.

In an aspect of the magnetic tape apparatus 10, the deviation amount isdetermined in accordance with the result obtained by reading the servopatterns 32 by the servo element pair 36. Therefore, in the magnetictape apparatus 10, it is possible to easily determine the deviationamount, compared to a case where the servo patterns 32 are not appliedto the magnetic tape MT.

In an aspect of the magnetic tape apparatus 10, the reading operation bythe reading element unit 38 is performed synchronously with the readingoperation by the servo element pair 36. Therefore, in the magnetic tapeapparatus 10, it is possible to instantaneously reduce the noisecomponent generated due to entering the reading target track from theadjacent track in the width direction of the magnetic tape, compared toa case of a magnetic disk and a magnetic tape in a helical scanningmethod, in which a servo pattern and data cannot be synchronously read.

In an aspect of the magnetic tape apparatus 10, the extraction unit 62includes the two-dimensional FIR filter 71. Each result obtained byperforming the waveform equalization process with respect to each of thefirst reading signal and the second reading signal is composed by thetwo-dimensional FIR filter 71, and accordingly, the data derived fromthe reading target track 30A is extracted from the first reading signaland the second reading signal. Therefore, in the magnetic tape apparatus10, it is possible to rapidly extract the data derived from the readingtarget track 30A from the first reading signal and the second readingsignal, compared to a case of using only a one-dimensional FIR filter.In addition, in the magnetic tape apparatus 10, it is possible torealize an operation due to a smaller operation amount, compared to acase of performing a matrix operation.

In an aspect of the magnetic tape apparatus 10, the first readingelement 40 and the second reading element 42 are used as a pair ofreading elements. Therefore, in the magnetic tape apparatus 10, it ispossible to contribute to miniaturization of the reading element unit38, compared to a case of using three or more reading elements. Byminiaturizing the reading element unit 38, the reading unit 26 and thereading head 16 can also be miniaturized. In addition, in the magnetictape apparatus 10, it is also possible to prevent occurrence of asituation in which the reading element units 38 adjacent to each otherare in contact with each other.

In an aspect of the magnetic tape apparatus 10, each of the plurality ofreading element units 38 reads data from the corresponding readingtarget track 30A included in each of the plurality of specific trackregions 31 by the linear scanning method. Therefore, in the magnetictape apparatus 10, it is possible to rapidly complete the reading ofdata from the plurality of reading target tracks 30A, compared to a casewhere the data is read by only the single reading element unit 38 fromeach of the plurality of reading target tracks 30A.

In the aspect, in a default state of the magnetic tape apparatus 10,each of the first reading element 40 and the second reading element 42is provided to straddle over both of the reading target track 30A andthe first noise mixing source track 30B, here, the magnetic tapeapparatus is not limited to the aspect. In an example shown in FIG. 12,a reading element unit 138 is used instead of the reading element unit38 described above. The reading element unit 138 comprises a firstreading element 140 and a second reading element 142. In a default stateof the magnetic tape apparatus 10, the center of the first readingelement 140 in the tape width direction coincides with a center CL ofthe reading target track 30A in the tape width direction. In a defaultstate of the magnetic tape apparatus 10, the first reading element 140and the second reading element 142 fall in the reading target track 30A,without being protruded to the first noise mixing source track 30B andthe second noise mixing source track 30C. In addition, in a defaultstate of the magnetic tape apparatus 10, parts of the first readingelement 140 and the second reading element 142 are provided to beoverlapped each other in the running direction, in the same manner asthe case of the first reading element 40 and the second reading element42 described in the embodiment.

As shown in FIG. 12 as an example, even in a state where the firstreading element 140 and the second reading element 142 face the readingtarget track 30A, without being protruded from the reading target track30A, a positional relationship between the reading element unit 138 andthe magnetic tape MT may be changed. That is, the reading element unit138 may straddle over the reading target track 30A and the first noisemixing source track 30B, or the reading element unit 138 may straddleover the reading target track 30A and the second noise mixing sourcetrack 30C. Even in these cases, by performing the processes in the stepS102 to the step S112 described above, it is possible to obtain the datacorresponding to the reading target track data, from which the noisecomponent from the first noise mixing source track 30B or the secondnoise mixing source track 30C is removed.

In addition, the first reading element 140 and the second readingelement 142 are disposed at position where parts thereof are overlappedeach other in the running direction, and accordingly, the second readingelement 142 can read the data from a portion of the reading target track30A where the reading cannot be performed by the first reading element140. As a result, it is possible to increase reliability of the readingtarget track data, compared to a case where the first reading element140 singly reads the data from the reading target track 30A.

As shown in FIG. 11 as an example, in a default state of the magnetictape apparatus 10, each of the first reading element 40 and the secondreading element 42 may be disposed at a position straddling over both ofthe reading target track 30A and the second noise mixing source track30C.

As described above, the reading element unit 38 including the firstreading element 40 and the second reading element 42 has been described.However, the magnetic tape apparatus is not limited to the aspect. In anexample shown in FIG. 13, a reading element unit 238 may be used insteadof the reading element unit 38. The reading element unit 238 isdifferent from the reading element unit 38, in a point that a thirdreading element 244 is included. In a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at a positionwhere a part thereof is overlapped with a part of the first readingelement 40 in the running direction. In addition, in a default state ofthe magnetic tape apparatus 10, the third reading element 244 isdisposed at a position to straddle over the reading target track 30A andthe second noise mixing source track 30C.

In this case, a third equalizer (not shown) is also allocated to thethird reading element 244, in the same manner as a case where the firstequalizer 70 is allocated to the first reading element 40 and the secondequalizer 72 is allocated to the second reading element 42. The thirdequalizer also has the same function as that of each of the firstequalizer and the second equalizer described above, and performs awaveform equalization process with respect to a third reading signalobtained by reading performed by the third reading element 244. Thethird equalizer performs, for example, a convolution arithmeticoperation of a tap coefficient with respect to the third reading signaland outputs the third arithmetic operation processed signal which is asignal after the arithmetic operation. The adder 44 adds and composes afirst arithmetic operation processed signal corresponding to the firstreading signal, a second arithmetic operation processed signalcorresponding to the second reading signal, the third arithmeticoperation processed signal corresponding to the third reading signal,and outputs the composite data obtained by the composite to the decodingunit 69.

In the example shown in FIG. 13, in a default state of the magnetic tapeapparatus 10, the third reading element 244 is disposed at the positionstraddling over the reading target track 30A and the second noise mixingsource track 30C, but the technique of the present disclosure is notlimited thereto. In a default state of the magnetic tape apparatus 10,the third reading element 244 may be disposed at the position facing thereading target track 30A, without being protruded from the readingtarget track 30A.

As described above, the reading element unit 38 has been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, the reading element pair 50 shown in FIG. 4 may be used insteadof the reading element unit 38. In this case, the first reading element50A and the second reading element 50B are set to be disposed atpositions adjacent to each other in the tape width direction. Inaddition, the first reading element 50A and the second reading element50B are set to be disposed in a line in the tape width direction so thatthe SNR of the composite data is higher than the SNR of the singlereading element data over the entire range of the track off-set, asshown in FIG. 6 as an example, without being in contact with each other.

In the example shown in FIG. 4, for example, the first reading element50A falls in the second track 49B in a plan view, and the second readingelement 50B falls in the first track 49A in a plan view.

As described above, the servo element pair 36 has been described.However, the magnetic tape apparatus is not limited to the aspect. Forexample, one of the servo elements 36A and 36B may be used instead ofthe servo element pair 36.

As described above, the aspect in which the plurality of specific trackregions 31 are arranged in the track region 30 at regular interval inthe tape width direction has been described. However, the magnetic tapeapparatus is not limited to the aspect. For example, in two specifictrack regions 31 adjacent to each other in the plurality of specifictrack regions 31, one specific track region 31 and the other specifictrack region 31 may be arranged in the tape width direction so as to beoverlapped by the area of one track in the tape width direction. In thiscase, one adjacent track included in one specific track region 31 (forexample, the first noise mixing source track 30B) becomes the readingtarget track 30A in the other specific track region 31. In addition, thereading target track 30A included in one specific track region 31becomes the adjacent track region (for example, the second noise mixingsource track 30C) in the other specific track region 31.

The configuration of the magnetic tape apparatus and the magnetic tapereading process described above are merely an example. Accordingly,unnecessary steps can be removed, new steps can be added, and theprocess procedure can be changed, within a range not departing from thegist.

The magnetic tape apparatus can perform the reading (reproducing) ofdata recorded on the magnetic tape, and can also have a configurationfor recording data on the magnetic tape.

Magnetic Tape

Next, the details of a magnetic tape according to an aspect of thepresent invention will be described.

The magnetic tape according to the aspect of the present invention has anon-magnetic support; and a magnetic layer including ferromagneticpowder and a binding agent. The magnetic layer has a timing-based servopattern, an edge shape of the timing-based servo pattern, specified bymagnetic force microscopy is a shape in which a difference(L_(99.9)−L_(0.1)) between a value L_(99.9) of a cumulative distributionfunction of 99.9% and a value L_(0.1) of a cumulative distributionfunction of 0.1% in a position deviation width from an ideal shape ofthe magnetic tape in a longitudinal direction is 180 nm or less, and theisoelectric point of a surface zeta potential of the magnetic layer is3.8 or less.

In recent years, a timing-based servo type has been widely used as asystem that uses a head tracking servo using a servo signal(hereinafter, referred to as a “servo system”). In the servo system of atiming-based servo type (hereinafter, referred to as a “timing-basedservo system”), a plurality of servo patterns having two or moredifferent shapes are formed on the magnetic layer, and a servo elementrecognizes a position of the servo element based on time interval atwhich two servo patterns having different shapes are reproduced (read)and time interval at which two servo patterns having the same shape arereproduced.

The “timing-based servo pattern” in the present invention and thisspecification refers to a servo pattern in which head tracking ispossible in the timing-based servo system. A servo pattern in which headtracking is possible in the timing-based servo system, as a plurality ofservo patterns having two or more different shapes, is formed on themagnetic layer by a servo write head that is a head for forming theservo pattern. In an example, the plurality of servo patterns having twoor more different shapes are continuously disposed at constant intervalfor each of the plurality of servo patterns having the same shape. Inanother example, different types of servo patterns are alternatelydisposed. Regarding the servo patterns having the same shape, positiondeviation in an edge shape of the servo patterns is ignored. The shapeof the servo pattern in which head tracking is possible in thetiming-based servo system and the disposition on the servo band areknown, and a specific aspect will be described later. Hereinafter, thetiming-based servo pattern is also simply referred to as a servopattern. In the present invention and this specification, an edge shapeof the timing-based servo pattern, specified by magnetic forcemicroscopy is also referred to as a shape of an edge (end side) locatedon a downstream side in a magnetic tape running direction (hereinafter,referred to simply as a “running direction”) in a case where data(information) is recorded.

Next, in the present invention and this specification, an edge shape ofthe timing-based servo pattern, specified by magnetic force microscopy,a difference (L_(99.9)−L_(0.1)) between a value L_(99.9) of a cumulativedistribution function of 99.9% and a value L_(0.1) of a cumulativedistribution function of 0.1% in a position deviation width of the edgeshape from an ideal shape of the magnetic tape in a longitudinaldirection, and an ideal shape will be described.

Hereinafter, a linear servo pattern that continuously extends from oneside toward the other side of the magnetic tape in a width direction andis inclined at an angle α with respect to a width direction of themagnetic tape will be mainly described as an example. The angle α refersto an angle formed by a line segment connecting two end portions in atape width direction of the edge of the servo pattern located on adownstream side with respect to a running direction of the magnetic tapein a case where data (information) is recorded, and a width direction ofthe magnetic tape. This will be further described below including thispoint.

For example, in a magnetic tape applied in a linear scanning methodwidely used as a recording method of the magnetic tape apparatus, ingeneral, a plurality of regions in each of which a servo pattern isformed (referred to as a “servo band”) exist on the magnetic layer alonga longitudinal direction of the magnetic tape. A region interposedbetween two servo bands is referred to as a data band. The recording ofinformation (magnetic signal) is performed on the data band, and aplurality of data tracks are formed on each data band along alongitudinal direction. FIG. 14 shows a disposition example of a databand and a servo band. In FIG. 14, in the magnetic layer of the magnetictape MT, a plurality of servo bands 1 are disposed between the guidebands 3. A plurality of regions 2 each of which is interposed betweentwo servo bands are data bands. The servo pattern is a magnetizationregion, and is formed by magnetizing a specific region of the magneticlayer with the servo write head. A region magnetized by the servo writehead (a position where the servo pattern is formed) is determined by thestandard. For example, in an LTO Ultrium format tape which is based on alocal standard, a plurality of servo patterns tilted with respect to atape width direction as shown in FIG. 15 are formed on a servo band, ina case of manufacturing a magnetic tape. Specifically, in FIG. 15, aservo frame SF on the servo band 1 is configured with a servo sub-frame1 (SSF1) and a servo sub-frame 2 (SSF2). The servo sub-frame 1 isconfigured with an A burst (in FIG. 15, reference numeral A) and a Bburst (in FIG. 15, reference numeral B). The A burst is configured withservo patterns A1 to A5 and the B burst is configured with servopatterns B1 to B5. Meanwhile, the servo sub-frame 2 is configured with aC burst (in FIG. 15, reference numeral C) and a D burst (in FIG. 15,reference numeral D). The C burst is configured with servo patterns C1to C4 and the D burst is configured with servo patterns D1 to D4. Such18 servo patterns are disposed in the sub-frames in the arrangement of5, 5, 4, 4, as the sets of 5 servo patterns and 4 servo patterns, andare used for recognizing the servo frames. Although one servo frame isshown in FIG. 15, a plurality of servo frames are disposed in each servoband in a running direction. In FIG. 15, an arrow shows a runningdirection. A running direction side of the arrow is an upstream side,and the opposite side is a downstream side.

FIGS. 16 and 17 are views for describing an angle α. In the servopattern shown in FIG. 15, in the servo pattern that is inclined towardan upstream side in a running direction like servo patterns A1 to A5 andC1 to C4, an angle formed by a line segment connecting two end portionsof a downstream edge E_(L) (a broken line L1 in FIG. 16) and a tapewidth direction (a broken line L2 in FIG. 16) is defined as an angle α.On the other hand, in the servo pattern that is inclined toward adownstream side in a running direction like servo patterns B1 to B5 andD1 to D4, an angle formed by a line segment connecting two end portionsof a downstream edge E_(L) (a broken line L1 in FIG. 17) and a tapewidth direction (a broken line L2 in FIG. 17) is defined as an angle α.This angle α is generally referred to as an azimuth angle and isdetermined by the setting of the servo write head in a case of forming amagnetization region (servo pattern) on the servo band.

In a case where the magnetization region (servo pattern) is formed on aservo band, in a case where the servo pattern is ideally formed, an edgeshape of the servo pattern inclined at an angle α with respect to themagnetic tape width direction coincides with a shape of a line segmentconnecting the two end portions of the edge (a broken line L1 in FIGS.16 and 17). That is, the shape becomes a straight line. Therefore, ateach portion on the edge, the position deviation width from the idealshape of the magnetic tape in a longitudinal direction (hereinafter,also simply referred to as “position deviation width”) becomes zero. Onthe other hand, as shown in an example in FIG. 18, an edge shape of theservo pattern may deviate from the ideal shape. The difference(L_(99.9)-L_(0.1)) is a value to be an index that the position deviationwidth from the ideal shape is small at each edge position of the servopattern and that variation in the position deviation width at each edgeportion is small. The difference (L_(99.9)-L_(0.1)) is a value obtainedby the following method.

A magnetic layer surface of the magnetic tape on which the servo patternis formed is observed with a magnetic force microscope (MFM). Ameasurement range is a range including five servo patterns. For example,in an LTO Ultrium format tape, five servo patterns of the A burst or theB burst can be observed by setting the measurement range to 90 μm×90 μm.A servo pattern (magnetization region) is extracted by measuring themeasurement range at a 100 nm pitch (rough measurement). In the presentinvention and this specification, the “magnetic layer surface” isidentical to a surface of the magnetic tape on a magnetic layer side.

Thereafter, in order to detect a boundary between the magnetizationregion and the non-magnetization region at the edge of the servo patternlocated on a downstream side with respect to a running direction, amagnetic profile is obtained by performing measurement at a 5 nm pitchin the vicinity of the boundary. In a case where the obtained magneticprofile is inclined at an angle α with respect to a width direction ofthe magnetic tape, the magnetic profile is rotationally corrected byanalysis software so as to be along the magnetic tape width direction(α=0°). Thereafter, position coordinates of a peak value of each profilemeasured at a 5 nm pitch are calculated by analysis software. Theposition coordinates of this peak value indicate a position of aboundary between the magnetization region and the non-magnetizationregion. The position coordinates are specified by, for example, an xycoordinate system in which a running direction is an x coordinate and awidth direction is a y coordinate.

In an example of a case where the ideal shape is a straight line andposition coordinates of a certain position on the straight line are (x,y)=(a, b), in a case where the edge shape actually obtained (positioncoordinates of the boundary) is coincident with an ideal shape, thecalculated position coordinates are (x, y)=(a, b). In this case, aposition deviation width is zero. On the other hand, in a case where theedge shape actually obtained is deviated from an ideal shape, thex-coordinate of the position of y=b of the boundary is x=a+c or x=a−c.x=a+c is, for example, a case where a width c is deviated on an upstreamside with respect to a running direction, and x=a−c is, for example, acase where a width c is deviated on a downstream side with respect to arunning direction (that is, −c on the basis of the upstream side). Here,c is a position deviation width. That is, an absolute value of aposition deviation width of the x coordinate from an ideal shape is aposition deviation width from the ideal shape of the magnetic tape inthe longitudinal direction. Thus, a position deviation width at eachedge portion on a downstream side of the running direction of themagnetic profile obtained by measurement at 5 nm pitch is obtained.

From the values obtained for each servo pattern, the cumulativedistribution function is obtained by analysis software. From theobtained cumulative distribution function, the value L_(99.9) of acumulative distribution function of 99.9% and the value L_(0.1) of acumulative distribution function of 0.1% are obtained, and a difference(L_(99.9)−L_(0.1)) is obtained for each servo pattern from the obtainedvalues.

The above measurement is performed in three different measurement ranges(the number of measurements N=3).

An arithmetic average of differences (L_(99.9)−L_(0.1)) obtained foreach servo pattern is defined as the above difference (L_(99.9)−L_(0.1))for the magnetic tape.

The “ideal shape” of an edge shape of the servo pattern in the presentinvention and this specification refers to an edge shape in a case wherethe servo pattern is formed without position deviation. For example, inan aspect, the servo pattern is a linear servo pattern extendingcontinuously or discontinuously from one side toward the other side ofthe magnetic tape in a width direction. The “linear” for the servopattern refers to that the pattern shape does not include a curvedportion regardless of position deviation of the edge shape. “Continuous”refers to extending from one side toward the other side in a tape widthdirection without an inflection point of a tilt angle and withoutinterruption. An example of the servo pattern extending continuouslyfrom one side toward the other side of the magnetic tape in a widthdirection is a servo pattern shown in FIG. 15. With respect to this,“discontinuous” refers to that there is one or more inflection points ofa tilt angle and/or extending interruptedly at one or more portions. Theshape that extends without interruption even though there is aninflection point of the tilt angle is a so-called polygonal line shape.An example of the discontinuous servo pattern extending from one sidetoward the other side in a tape width direction with one inflectionpoint of the tilt angle and without interruption is a servo patternshown in FIG. 19. On the other hand, an example of the discontinuousservo pattern extending from one side toward the other side in a tapewidth direction without an inflection point of the tilt angle and withinterruption at one portion is a servo pattern shown in FIG. 20. Inaddition, an example of the discontinuous servo pattern extending fromone side toward the other side in a tape width direction with oneinflection point of the tilt angle and with interruption at one portionis a servo pattern shown in FIG. 21.

In a linear servo pattern that continuously extends from one side towardthe other side in a tape width direction, the “ideal shape” of the edgeshape is a shape of a line segment connecting two end portions of anedge on a downstream side in a running direction of the linear servopattern (a linear shape). For example, the linear servo pattern shown inFIG. 15 has a shape of a straight line indicated by L1 in FIG. 16 or 17.On the other hand, in a linear servo pattern that extendsdiscontinuously, the ideal shape is a shape of a line segment connectingone end and the other end of a portion with the same tilt angle (alinear shape) in a shape with an inflection point of the tilt angle. Inaddition, in the shape extending with interruption at one or moreportions, the ideal shape is a shape of a line segment connecting oneend and the other end of each continuously extending portion (linearshape). For example, in the servo pattern shown in FIG. 19, the idealshape is a shape of a line segment connecting e1 and e2, and a linesegment connecting e2 and e3. In the servo pattern shown in FIG. 20, theideal shape is a shape of a line segment connecting e4 and e5, and aline segment connecting e6 and e7. In the servo pattern shown in FIG.21, the ideal shape is a shape of a line segment connecting e8 and e9,and a line segment connecting e10 and e11.

In the above, a linear servo pattern has been described as an example.Here, the servo pattern may be a servo pattern in which an ideal shapeof the edge shape is a curved shape. For example, in a servo pattern inwhich an edge shape on a downstream side with respect to a runningdirection is ideally a partial arc shape, it is possible to obtain adifference (L_(99.9)−L_(0.1)) from a position deviation width, of anedge shape on a downstream side with respect to a running direction,obtained from the position coordinates obtained by a magnetic forcemicroscope, with respect to position coordinates of this partial arc.

As a magnetic force microscope used in the above measurement, acommercially available or known magnetic force microscope is used in afrequency modulation (FM) mode. As a probe of a magnetic forcemicroscope, for example, SSS-MFMR (nominal curvature radius 15 nm)manufactured by Nanoworld AG can be used. A distance between a magneticlayer surface and a probe distal end during magnetic force microscopy isin a range of 20 to 50 nm.

In addition, as analysis software, commercially available analysissoftware or analysis software in which a known arithmetic expression isincorporated can be used.

Next, a measurement method of the isoelectric point of the surface zetapotential of the magnetic layer will be described. In the presentinvention and this specification, the “magnetic layer surface” isidentical to a surface of the magnetic tape on a magnetic layer side.

In the present invention and this specification, the isoelectric pointof the surface zeta potential of the magnetic layer is a value of pH ina case where a surface zeta potential measured by a flow potentialmethod (also referred to as a flow current method) becomes zero. Asample is cut out from the magnetic tape which is a measurement target,and the sample is disposed in a measurement cell so that the magneticlayer surface comes into contact with an electrolyte. Pressure in themeasurement cell is changed to flow the electrolyte and a flow potentialat each pressure is measured, and then, the surface zeta potential isobtained by the following calculation expression.

$\begin{matrix}{\zeta = {\frac{dI}{dp} \times \frac{\eta}{{ɛɛ}_{0}}\frac{L}{A}}} & {{Calculation}\mspace{14mu} {Expression}}\end{matrix}$

[ζ: surface zeta potential, p: pressure, I: flow potential, η: viscosityof electrolyte, ε: relative dielectric constant of electrolyte, ε₀:dielectric constant in a vacuum state, L: length of channel (flow pathbetween two electrodes), A: area of cross section of channel]

The pressure is changed in a range of 0 to 400,000 Pa (0 to 400 mbar).The calculation of the surface zeta potential by flowing the electrolyteto the measurement cell and measuring a flow potential is performedusing the electrolytes having different pH (from pH 9 to pH 3 atinterval of about 0.5). A total number of measurement points is 13 fromthe measurement point of pH 9 to the 13th measurement point of pH 3. Bydoing so, the surface zeta potential is obtained for each measurementpoint of pH. As pH decreases, the surface zeta potential decreases.Thus, two measurement points at which polarity of the surface zetapotential changes (a change from a positive value to a negative value)may appear, while pH decreases from 9 to 3. In a case where such twomeasurement points appear, using a straight line (linear function)showing a relationship between the surface zeta potential and pH of eachof the two measurement points, pH in a case where the surface zetapotential is zero is obtained by interpolation. Meanwhile, in a casewhere all of the surface zeta potentials obtained during the decrease ofpH from 9 to 3 is positive value, using a straight line (linearfunction) showing a relationship between the surface zeta potential andpH of the 13th measurement point (pH 3) which is the final measurementpoint and the 12th measurement point, the pH in a case where the surfacezeta potential is zero is obtained by extrapolation. On the other hand,in a case where all of the surface zeta potentials obtained during thedecrease of pH from 9 to 3 is negative value, using a straight line(linear function) showing a relationship between the surface zetapotential and pH of the first measurement point (pH 9) which is thefinal measurement point and the 12th measurement point, pH in a casewhere the surface zeta potential is zero is obtained by extrapolation.By doing so, the value of pH in a case where the surface zeta potentialof the magnetic layer measured by the flow potential method becomes zerois obtained.

The above measurement is performed three times in total at roomtemperature by using different samples cut out from the same magnetictape (magnetic tape which is a measurement target), and pH in a casewhere the surface zeta potential becomes zero in each measurement isobtained. For the viscosity and the relative dielectric constant of theelectrolyte, a measurement value at room temperature is used. The roomtemperature is set as a range from 20° C. to 27° C. Regarding themagnetic layer, an arithmetic average of three pHs obtained as describedabove is an isoelectric point of the surface zeta potential of themagnetic layer of the magnetic tape which is a measurement target. Asthe electrolyte having pH 9, an electrolyte obtained by adjusting pH ofa KCl aqueous solution having a concentration of 1 mmol/L to pH 9 byusing a KOH aqueous solution having a concentration of 0.1 mol/L isused. As the electrolyte having other pH, an electrolyte obtained byadjusting pH of the electrolyte having pH 9, which is adjusted asdescribed above, by using an HCl aqueous solution having a concentrationof 0.1 mol/L is used. The isoelectric point of the surface zetapotential measured by the method described above is an isoelectric pointobtained regarding the magnetic layer surface.

It is considered that in a case of reading data recorded on the magnetictape, the magnetic layer surface comes into contact with the readingelement and the magnetic layer surface is scraped, and thus scrapings(may be referred to as debris) are generated. In a case where thesescrapings are strongly stuck to the magnetic layer surface, a contactstate between the magnetic layer surface and the reading element becomesunstable. The present inventors suppose that this causes a large changein a relative position (a relative positional change) between thereading element and the reading target track. With respect to this, thepresent inventors consider that in a case of using the magnetic layer ina range of acidic pH in which the isoelectric point of the surface zetapotential is 3.8 or less, a repulsive force may be easily appliedbetween the scrapings generated from the magnetic layer and the magneticlayer surface. It is supposed that preventing the scrapings from beingstrongly stuck to the magnetic layer surface by the repulsive forcecontributes to suppression of occurrence of the relative positionalchange. The present inventors consider that this aspect contributes to amore appropriate waveform equalization process performed on each of thereading results obtained by a plurality of the reading elements, andleads to an increase in an acceptable amount of a deviation amount (atrack off-set amount), for ensuring excellent reproducing quality.

In addition, as described above, it is considered that formation of aservo pattern in a shape closer to a design shape also leads to anincrease in an acceptable amount of a deviation amount (a track off-setamount), for ensuring excellent reproducing quality. In this regard, thepresent inventors consider that the above difference (L_(99.9)−L_(0.1))is an index related to a shape of the servo pattern, and the difference(L_(99.9)−L_(0.1)) of 180 nm or less contributes to an increase in anacceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality. Regarding a shape of a servopattern formed on the magnetic layer, as one of means for suppressingdeviation between a shape of a servo pattern (a magnetization region) tobe formed on the magnetic layer by applying a magnetic field by a servowrite head and a shape of a servo pattern actually formed on themagnetic layer, it is considered to increase a capacity of a servo writehead, specifically, to use a servo write head having a large magneticfield (leakage magnetic field). It is also considered that scrapings(debris) are generated in a case where a servo pattern is formed byapplying a magnetic field to the magnetic layer by the servo write headwhile contacting the magnetic layer surface. In a case where thescrapings are strongly stuck to the magnetic layer surface, a contactstate between the magnetic layer surface and the servo write headbecomes unstable. The present inventors suppose that this is a cause ofdeviation generated between a shape of the servo pattern (amagnetization region) to be formed on the magnetic layer by applying amagnetic field by the servo write head and a shape of a servo patternactually formed on the magnetic layer. With respect to this, the presentinventors consider that preventing the scrapings from being stronglystuck to the magnetic layer surface by the repulsive force appliedbetween the magnetic layer surface and the scrapings generated from themagnetic layer in a range of acidic pH in which the isoelectric point ofthe surface zeta potential is 3.8 or less contributes to formation of aservo pattern having a shape closer to a design shape, that is, thedifference (L_(99.9)-L_(0.1)) of 180 nm or less.

Here, the above description is merely supposition and the presentinvention is not limited thereto.

Hereinafter, the magnetic tape will be described later in detail.

Isoelectric Point of Surface Zeta Potential of Magnetic Layer

The isoelectric point of the surface zeta potential of the magneticlayer of the magnetic tape is 3.8 or less. It is supposed that thisaspect contributes to an increase in an acceptable amount of a deviationamount (a track off-set amount), for ensuring excellent reproducingquality. From the above viewpoint, the isoelectric point of the surfacezeta potential of the magnetic layer is preferably 3.7 or less, morepreferably 3.6 or less, still more preferably 3.5 or less, still morepreferably 3.4 or less, and still more preferably 3.3 or less.

As will be described later in detail, the isoelectric point of thesurface zeta potential of the magnetic layer can be controlled by thekind of a component used for forming the magnetic layer, a formationstep of the magnetic layer, and the like. From a viewpoint ofavailability of a component (for example, a binding agent) used forRaining the magnetic layer, the isoelectric point of the surface zetapotential of the magnetic layer is preferably 2.0 or more, morepreferably 2.5 or more, still more preferably 2.6 or more, and stillmore preferably 2.7 or more.

Difference (L_(99.9)−L_(0.1))

The difference (L_(99.9)−L_(0.1)) is 180 nm or less. It is supposed thatthis aspect also contributes to an increase in an acceptable amount of adeviation amount (a track off-set amount), for ensuring excellentreproducing quality. From the above viewpoint, the difference(L_(99.9)−L_(0.1)) is preferably 170 nm or less, more preferably 160 nmor less, and still more preferably 150 nm or less. Further, thedifference (L_(99.9)−L_(0.1)) may be, for example, 50 nm or more, 60 nmor more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more.Here, it is considered that the smaller a value of the difference(L_(99.9)−L_(0.1)) is, the more preferable it is to increase theacceptable amount of a deviation amount (a track off-set amount), forensuring excellent reproducing quality, and thus the difference(L_(99.9)−L_(0.1)) may be below the lower limit exemplified above.

Next, a magnetic layer of the magnetic tape, and the like will befurther described.

Magnetic Layer

Ferromagnetic Powder

A magnetic layer includes ferromagnetic powder and a binding agent. Asthe ferromagnetic powder included in the magnetic layer, knownferromagnetic powder that is ferromagnetic powder used in the magneticlayer of various magnetic recording media, may be used. It is preferableto use ferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density. In this respect, anaverage particle size of the ferromagnetic powder is preferably 50 nm orless, more preferably 45 nm or less, still more preferably 40 nm orless, still more preferably 35 nm or less, still more preferably 30 nmor less, still more preferably 25 nm or less, and still more preferably20 nm or less. On the other hand, from a viewpoint of magnetizationstability, an average particle size of the ferromagnetic powder ispreferably 5 nm or more, more preferably 8 nm or more, still morepreferably 10 nm or more, and still more preferably 15 nm or more, andstill more preferably 20 nm or more.

Hexagonal Ferrite Powder

Preferable specific examples of ferromagnetic powder may includehexagonal ferrite powder. For details of the hexagonal ferrite powder,descriptions disclosed in paragraphs 0012 to 0030 of JP2011-225417A,paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 ofJP2012-204726A, and paragraphs 0029 to 0084 of JP2015-127985A can bereferred to, for example.

In the present invention and this specification, “hexagonal ferritepowder” refers to ferromagnetic powder in which a hexagonal ferrite typecrystal structure is detected as a main phase by X-ray diffractionanalysis. The main phase refers to a structure to which the highestintensity diffraction peak in an X-ray diffraction spectrum obtained byX-ray diffraction analysis is attributed. For example, in a case wherethe highest intensity diffraction peak is attributed to a hexagonalferrite crystal structure in an X-ray diffraction spectrum obtained byX-ray diffraction analysis, it is determined that the hexagonal ferritecrystal structure is detected as the main phase. In a case where only asingle structure is detected by X-ray diffraction analysis, thisdetected structure is taken as the main phase. The hexagonal ferritetype crystal structure includes at least an iron atom, a divalent metalatom and an oxygen atom, as a constituent atom. The divalent metal atomis a metal atom that can be a divalent cation as an ion, and examplesthereof may include an alkaline earth metal atom such as a strontiumatom, a barium atom, and a calcium atom, a lead atom, and the like. Inthe present invention and this specification, hexagonal strontiumferrite powder means that a main divalent metal atom contained in thepowder is a strontium atom, and hexagonal barium ferrite powder meansthat a main divalent metal atom included in the powder is a barium atom.The main divalent metal atom refers to a divalent metal atom thataccounts for the most on an at % basis among divalent metal atomsincluded in the powder. Here, a rare earth atom is not included in theabove divalent metal atom. The “rare earth atom” in the presentinvention and this specification is selected from the group consistingof a scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. TheLanthanoid atom is selected from the group consisting of a lanthanumatom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymiumatom (Nd), a promethium atom (Pm), a samarium atom (Sm), a europium atom(Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom(Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), anytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, the hexagonal strontium ferrite powder which is an aspectof the hexagonal ferrite powder will be described in more detail.

An activation volume of the hexagonal strontium ferrite powder ispreferably in a range of 800 to 1600 nm³. The particulate hexagonalstrontium ferrite powder exhibiting an activation volume in the aboverange is suitable for manufacturing a magnetic tape exhibiting excellentelectromagnetic conversion characteristics. An activation volume of thehexagonal strontium ferrite powder is preferably 800 nm³ or more, andmay be, for example, 850 nm³ or more. Further, from a viewpoint offurther improving electromagnetic conversion characteristics, anactivation volume of the hexagonal strontium ferrite powder is morepreferably 1500 nm³ or less, still more preferably 1400 nm³ or less,still more preferably 1300 nm³ or less, still more preferably 1200 nm³or less, and still more preferably 1100 nm³ or less. The same applies toan activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and is anindex indicating a magnetic size of a particle. An activation volumedescribed in the present invention and this specification and ananisotropy constant Ku which will be described later are values obtainedfrom the following relational expression between a coercivity Hc and anactivation volume V, by performing measurement in an He measurementportion at a magnetic field sweep rate of 3 minutes and 30 minutes usinga vibrating sample magnetometer (measurement temperature: 23° C.±1° C.).In a unit of the anisotropy constant Ku, 1 erg/cc=1.0×10⁻¹ J/m³.

Hc=2Ku/Ms{1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the above formula, Ku: anisotropy constant (unit: J/m³), Ms:saturation magnetization (Unit: kA/m), k: Boltzmann constant, T:absolute temperature (unit: K), V: activation volume (unit: cm³), A:spin precession frequency (unit: s⁻¹), t: magnetic field reversal time(unit: s)]

An index for reducing thermal fluctuation, in other words, improvingthermal stability may include an anisotropy constant Ku. The hexagonalstrontium ferrite powder may preferably have Ku of 1.8×10⁵ J/m³ or more,and more preferably have a Ku of 2.0×10⁵ J/m³ or more. Ku of thehexagonal strontium ferrite powder may be, for example, 2.5×10⁵ J/m³ orless. Here, it means that the higher Ku is, the higher thermal stabilityis, this is preferable, and thus, a value thereof is not limited to thevalues exemplified above.

The hexagonal strontium ferrite powder may or may not include a rareearth atom. In a case where the hexagonal strontium ferrite powderincludes a rare earth atom, it is preferable to include a rare earthatom at a content (bulk content) of 0.5 to 5.0 at % with respect to 100at % of an iron atom. In an aspect, the hexagonal strontium ferritepowder including a rare earth atom may have a rare earth atom surfacelayer portion uneven distribution property. In the present invention andthis specification, the “rare earth atom surface layer portion unevendistribution property” means that a rare earth atom content with respectto 100 at % of an iron atom in a solution obtained by partiallydissolving hexagonal strontium ferrite powder with an acid (hereinafter,referred to as a “rare earth atom surface layer portion content” orsimply a “surface layer portion content” for a rare earth atom) and arare earth atom content with respect to 100 at % of an iron atom in asolution obtained by totally dissolving hexagonal strontium ferritepowder with an acid (hereinafter, referred to as a “rare earth atom bulkcontent” or simply a “bulk content” for a rare earth atom) satisfy aratio of a rare earth atom surface layer portion content/a rare earthatom bulk content >1.0. A rare earth atom content in hexagonal ferritepowder which will be described later is the same meaning as the rareearth atom bulk content. On the other hand, partial dissolution using anacid dissolves a surface layer portion of a particle configuringhexagonal strontium ferrite powder, and thus, a rare earth atom contentin a solution obtained by partial dissolution is a rare earth atomcontent in a surface layer portion of a particle configuring hexagonalstrontium ferrite powder. A rare earth atom surface layer portioncontent satisfying a ratio of “rare earth atom surface layer portioncontent/rare earth atom bulk content >1.0” means that in a particle ofhexagonal strontium ferrite powder, rare earth atoms are unevenlydistributed in a surface layer portion (that is, more than in aninside). The surface layer portion in the present invention and thisspecification means a partial region from a surface of a particleconfiguring hexagonal strontium ferrite powder toward an inside.

In a case where hexagonal ferrite powder includes a rare earth atom, arare earth atom content (bulk content) is preferably in a range of 0.5to 5.0 at % with respect to 100 at % of an iron atom. It is consideredthat a bulk content in the above range of the included rare earth atomand uneven distribution of the rare earth atoms in a surface layerportion of a particle configuring hexagonal strontium ferrite powdercontribute to suppression of a decrease in a reproducing output inrepeated reproduction. It is supposed that this is because hexagonalstrontium ferrite powder includes a rare earth atom with a bulk contentin the above range, and rare earth atoms are unevenly distributed in asurface layer portion of a particle configuring hexagonal strontiumferrite powder, and thus it is possible to increase an anisotropyconstant Ku. The higher a value of an anisotropy constant Ku is, themore a phenomenon of so-called thermal fluctuation can be suppressed (inother words, thermal stability can be improved). By suppressingoccurrence of thermal fluctuation, it is possible to suppress a decreasein reproducing output during repeated reproduction. It is supposed thatuneven distribution of rare earth atoms in a particulate surface layerportion of hexagonal strontium ferrite powder contributes tostabilization of spins of iron (Fe) sites in a crystal lattice of asurface layer portion, and thus, an anisotropy constant Ku may beincreased.

Moreover, it is supposed that the use of hexagonal strontium ferritepowder having a rare earth atom surface layer portion unevendistribution property as a ferromagnetic powder in the magnetic layeralso contributes to inhibition of a surface of the magnetic layer frombeing scraped by being slid with respect to the magnetic head. That is,it is supposed that hexagonal strontium ferrite powder having rare earthatom surface layer portion uneven distribution property can alsocontribute to an improvement of running durability of the magnetic tape.It is supposed that this may be because uneven distribution of rareearth atoms on a surface of a particle configuring hexagonal strontiumferrite powder contributes to an improvement of interaction between theparticle surface and an organic substance (for example, a binding agentand/or an additive) included in the magnetic layer, and, as a result, astrength of the magnetic layer is improved.

From a viewpoint of further suppressing a decrease in reproducing outputduring repeated reproduction and/or a viewpoint of further improving therunning durability, the rare earth atom content (bulk content) is morepreferably in a range of 0.5 to 4.5 at %, still more preferably in arange of 1.0 to 4.5 at %, and still more preferably in a range of 1.5 to4.5 at %.

The bulk content is a content obtained by totally dissolving hexagonalstrontium ferrite powder. In the present invention and thisspecification, unless otherwise noted, the content of an atom means abulk content obtained by totally dissolving hexagonal strontium ferritepowder. The hexagonal strontium ferrite powder including a rare earthatom may include only one kind of rare earth atom as the rare earthatom, or may include two or more kinds of rare earth atoms. The bulkcontent in the case of including two or more types of rare earth atomsis obtained for the total of two or more types of rare earth atoms. Thisalso applies to other components in the present invention and thisspecification. That is, unless otherwise noted, a certain component maybe used alone or in combination of two or more. A content amount orcontent in a case where two or more components are used refers to thatfor the total of two or more components.

In a case where the hexagonal strontium ferrite powder includes a rareearth atom, the included rare earth atom may be any one or more of rareearth atoms. As a rare earth atom that is preferable from a viewpoint offurther suppressing a decrease in reproducing output in repeatedreproduction, there are a neodymium atom, a samarium atom, an yttriumatom, and a dysprosium atom, here, a neodymium atom, a samarium atom,and an yttrium atom are more preferable, and a neodymium atom is stillmore preferable.

In the hexagonal strontium ferrite powder having a rare earth atomsurface layer portion uneven distribution property, the rare earth atomsmay be unevenly distributed in the surface layer portion of a particleconfiguring the hexagonal strontium ferrite powder, and the degree ofuneven distribution is not limited. For example, for a hexagonalstrontium ferrite powder having a rare earth atom surface layer portionuneven distribution property, a ratio between a surface layer portioncontent of a rare earth atom obtained by partial dissolution underdissolution conditions which will be described later and a bulk contentof a rare earth atom obtained by total dissolution under dissolutionconditions which will be described later, that is, “surface layerportion content/bulk content” exceeds 1.0 and may be 1.5 or more. A“surface layer portion content/bulk content” larger than 1.0 means thatin a particle configuring the hexagonal strontium ferrite powder, rareearth atoms are unevenly distributed in the surface layer portion (thatis, more than in the inside). Further, a ratio between a surface layerportion content of a rare earth atom obtained by partial dissolutionunder dissolution conditions which will be described later and a bulkcontent of a rare earth atom obtained by total dissolution under thedissolution conditions which will be described later, that is, “surfacelayer portion content/bulk content” may be, for example, 10.0 or less,9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0or less. Here, in the hexagonal strontium ferrite powder having a rareearth atom surface layer portion uneven distribution property, the rareearth atoms may be unevenly distributed in the surface layer portion ofa particle configuring the hexagonal strontium ferrite powder, and the“surface layer portion content/bulk content” is not limited to theillustrated upper limit or lower limit.

The partial dissolution and the total dissolution of the hexagonalstrontium ferrite powder will be described below. For the hexagonalstrontium ferrite powder that exists as a powder, the partially andtotally dissolved sample powder is taken from the same lot of powder. Onthe other hand, for the hexagonal strontium ferrite powder included inthe magnetic layer of the magnetic tape, a part of the hexagonalstrontium ferrite powder taken out from the magnetic layer is subjectedto partial dissolution, and the other part is subjected to totaldissolution. The hexagonal strontium ferrite powder can be taken outfrom the magnetic layer by a method disclosed in a paragraph 0032 of3P2015-091747A, for example.

The partial dissolution means that dissolution is performed such that,at the end of dissolution, the residue of the hexagonal strontiumferrite powder can be visually checked in the solution. For example, bypartial dissolution, it is possible to dissolve a region of 10 to 20mass % of the particle configuring the hexagonal strontium ferritepowder with the total particle being 100 mass %. On the other hand, thetotal dissolution means that dissolution is performed such that, at theend of dissolution, the residue of the hexagonal strontium ferritepowder can not be visually checked in the solution.

The partial dissolution and measurement of the surface layer portioncontent are performed by the following method, for example. Here, thefollowing dissolution conditions such as an amount of sample powder areillustrative, and dissolution conditions for partial dissolution andtotal dissolution can be employed in any manner.

A container (for example, a beaker) containing 12 mg of sample powderand 10 ml of 1 mol/L hydrochloric acid is held on a hot plate at a settemperature of 70° C. for 1 hour. The obtained solution is filtered by amembrane filter of 0.1 μm. Elemental analysis of the filtrated solutionis performed by an inductively coupled plasma (ICP) analyzer. In thisway, the surface layer portion content of a rare earth atom with respectto 100 at % of an iron atom can be obtained. In a case where a pluralityof types of rare earth atoms are detected by elemental analysis, thetotal content of all rare earth atoms is defined as the surface layerportion content. This also applies to the measurement of the bulkcontent.

On the other hand, the total dissolution and measurement of the bulkcontent are performed by the following method, for example.

A container (for example, a beaker) containing 12 mg of sample powderand 10 ml of 4 mol/L hydrochloric acid is held on a hot plate at a settemperature of 80° C. for 3 hours. Thereafter, the method is carried outin the same manner as the partial dissolution and the measurement of thesurface layer portion content, and the bulk content with respect to 100at % of an iron atom can be obtained.

From a viewpoint of increasing the reproducing output in a case ofreproducing information recorded on the magnetic tape, it is desirablethat mass magnetization as of the ferromagnetic powder included in themagnetic tape is high. In this regard, the hexagonal strontium ferritepowder including a rare earth atom but not having the rare earth atomsurface layer portion uneven distribution property tends to have aslargely lower than the hexagonal strontium ferrite powder including norare earth atom. On the other hand, it is considered that hexagonalstrontium ferrite powder having a rare earth atom surface layer portionuneven distribution property is preferable in suppressing such a largedecrease in σs. In an aspect, σs of the hexagonal strontium ferritepowder may be 45 A·m²/kg or more, and may be 47 A·m²/kg or more. On theother hand, from a viewpoint of noise reduction, σs is preferably 80A·m²/kg or less and more preferably 60 A·m²/kg or less. σs can bemeasured using a known measuring device, such as a vibrating samplemagnetometer, capable of measuring magnetic properties. In the presentinvention and this specification, unless otherwise noted, the massmagnetization σs is a value measured at a magnetic field intensity of1194 kA/m (15 kOe).

Regarding the content (bulk content) of a constituent atom of thehexagonal ferrite powder, the strontium atom content may be, forexample, in a range of 2.0 to 15.0 at % with respect to 100 at % of aniron atom. In an aspect, in the hexagonal strontium ferrite powder, adivalent metal atom included in the powder may be only a strontium atom.In another aspect, the hexagonal strontium ferrite powder may includeone or more other divalent metal atoms in addition to a strontium atom.For example, a barium atom and/or a calcium atom may be included. In acase where another divalent metal atom other than a strontium atom isincluded, a barium atom content and a calcium atom content in thehexagonal strontium ferrite powder are, for example, in a range of 0.05to 5.0 at % with respect to 100 at % of an iron atom, respectively.

As a crystal structure of hexagonal ferrite, a magnetoplumbite type(also referred to as an “M type”), a W type, a Y type, and a Z type areknown. The hexagonal strontium ferrite powder may have any crystalstructure. The crystal structure can be checked by X-ray diffractionanalysis. In the hexagonal strontium ferrite powder, a single crystalstructure or two or more crystal structures may be detected by X-raydiffraction analysis. For example, according to an aspect, in thehexagonal strontium ferrite powder, only the M-type crystal structuremay be detected by X-ray diffraction analysis. For example, M-typehexagonal ferrite is represented by a composition formula of AFe₁₂O₁₉.Here, A represents a divalent metal atom, and in a case where thehexagonal strontium ferrite powder is the M-type, A is only a strontiumatom (Sr), or in a case where, as A, a plurality of divalent metal atomsare included, as described above, a strontium atom (Sr) accounts for themost on an at % basis. The divalent metal atom content of the hexagonalstrontium ferrite powder is usually determined by the type of crystalstructure of the hexagonal ferrite and is not particularly limited. Thesame applies to the iron atom content and the oxygen atom content. Thehexagonal strontium ferrite powder may include at least an iron atom, astrontium atom, and an oxygen atom, and may further include a rare earthatom. Furthermore, the hexagonal strontium ferrite powder may or may notinclude atoms other than these atoms. As an example, the hexagonalstrontium ferrite powder may include an aluminum atom (Al). A content ofan aluminum atom can be, for example, 0.5 to 10.0 at % with respect to100 at % of an iron atom. From a viewpoint of further suppressing adecrease in reproducing output in repeated reproduction, the hexagonalstrontium ferrite powder includes an iron atom, a strontium atom, anoxygen atom, and a rare earth atom, and the content of atoms other thanthese atoms is preferably 10.0 at % or less, more preferably in a rangeof 0 to 5.0 at %, and may be 0 at % with respect to 100 at % of an ironatom. That is, in an aspect, the hexagonal strontium ferrite powder maynot include atoms other than an iron atom, a strontium atom, an oxygenatom, and a rare earth atom. The content expressed in at % is obtainedby converting a content of each atom (unit: mass %) obtained by totallydissolving hexagonal strontium ferrite powder into a value expressed inat % using an atomic weight of each atom. Further, in the presentinvention and this specification, “not include” for a certain atom meansthat a content measured by an ICP analyzer after total dissolution is 0mass %. A detection limit of the ICP analyzer is usually 0.01 ppm (partper million) or less on a mass basis. The “not included” is used as ameaning including that an atom is included in an amount less than thedetection limit of the ICP analyzer. In an aspect, the hexagonalstrontium ferrite powder may not include a bismuth atom (Bi).

Metal Powder

As a preferred specific example of the ferromagnetic powder, aferromagnetic metal powder can also be used. For details of theferromagnetic metal powder, descriptions disclosed in paragraphs 0137 to0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A canbe referred to, for example.

ε-Iron Oxide Powder

As a preferred specific example of the ferromagnetic powder, ε-ironoxide powder can also be used. In the present invention and thisspecification, “ε-iron oxide powder” refers to ferromagnetic powder inwhich a ε-iron oxide type crystal structure is detected as a main phaseby X-ray diffraction analysis. For example, in a case where the highestintensity diffraction peak is attributed to a ε-iron oxide type crystalstructure in an X-ray diffraction spectrum obtained by X-ray diffractionanalysis, it is determined that the ε-iron oxide type crystal structureis detected as the main phase. As a manufacturing method of ε-iron oxidepowder, a manufacturing method from a goethite, a reverse micellemethod, and the like are known. All of the manufacturing methods arewell known. Regarding a method of manufacturing ε-iron oxide powder inwhich a part of Fe is substituted with substitutional atoms such as Ga,Co, Ti, Al, or Rh, a description disclosed in J. Jpn. Soc. PowderMetallurgy Vol. 61 Supplement, No. S1, pp. 5280 to 5284, J. Mater. Chem.C, 2013, 1, pp. 5200 to 5206 can be referred to, for example. Here, themanufacturing method of ε-iron oxide powder capable of being used as theferromagnetic powder in the magnetic layer of the magnetic tape is notlimited to the methods described here.

An activation volume of the ε-iron oxide powder is preferably in a rangeof 300 to 1500 nm³. The particulate ε-iron oxide powder exhibiting anactivation volume in the above range is suitable for manufacturing amagnetic tape exhibiting excellent electromagnetic conversioncharacteristics. An activation volume of the ε-iron oxide powder ispreferably 300 nm³ or more, and may be, for example, 500 nm³ or more.Further, from a viewpoint of further improving electromagneticconversion characteristics, an activation volume of the ε-iron oxidepowder is more preferably 1400 nm³ or less, still more preferably 1300nm³ or less, still more preferably 1200 nm³ or less, and still morepreferably 1100 nm³ or less.

An index for reducing thermal fluctuation, in other words, improvingthermal stability may include an anisotropy constant Ku. The ε-ironoxide powder preferably has Ku of 3.0×10⁴ J/m³ or more, and morepreferably has Ku of 8.0×10⁴ J/m³ or more. Ku of the ε-iron oxide powdermay be, for example, 3.0×10⁵ J/m³ or less. Here, it means that thehigher Ku is, higher thermal stability is, this is preferable, and thus,a value thereof is not limited to the values exemplified above.

From a viewpoint of increasing the reproducing output in a case ofreproducing information recorded on the magnetic tape, it is desirablethat mass magnetization σs of the ferromagnetic powder included in themagnetic tape is high. In this regard, in an aspect, as of the ε-ironoxide powder may be 8 A·m²/kg or more, and may be 12 A·m²/kg or more. Onthe other hand, from a viewpoint of noise reduction, σs of the ε-ironoxide powder is preferably 40 A·m²/kg or less and more preferably 35A·m²/kg or less.

In the present invention and this specification, unless otherwise noted,an average particle size of various powders such as the ferromagneticpowder is a value measured by the following method using a transmissionelectron microscope.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, and the image is printed on printingpaper so that the total magnification ratio becomes 500,000 to obtain animage of particles configuring the powder. A target particle is selectedfrom the obtained image of particles, an outline of the particle istraced with a digitizer, and a size of the particle (primary particle)is measured. The primary particle is an independent particle which isnot aggregated.

The measurement described above is performed regarding 500 particlesrandomly extracted. An arithmetic average of the particle sizes of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using a transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the present invention andthis specification, the powder means an aggregate of a plurality ofparticles. For example, ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. Further, the aggregate of theplurality of particles not only includes an aspect in which particlesconfiguring the aggregate directly come into contact with each other,but also includes an aspect in which a binding agent or an additivewhich will be described later is interposed between the particles. Theterm “particle” is used to describe a powder in some cases.

As a method of taking sample powder from the magnetic tape in order tomeasure the particle size, a method disclosed in a paragraph of 0015 ofJP2011-048878A can be used, for example.

In the present invention and this specification, unless otherwise noted,

-   -   (1) in a case where the shape of the particle observed in the        particle image described above is a needle shape, a fusiform        shape, or a columnar shape (here, a height is greater than a        maximum long diameter of a bottom surface), the size (particle        size) of the particles configuring the powder is shown as a        length of a long axis configuring the particle, that is, a long        axis length,    -   (2) in a case where the shape of the particle is a plate shape        or a columnar shape (here, a thickness or a height is smaller        than a maximum long diameter of a plate surface or a bottom        surface), the particle size is shown as a maximum long diameter        of the plate surface or the bottom surface, and    -   (3) in a case where the shape of the particle is a sphere shape,        a polyhedron shape, or an unspecified shape, and the long axis        configuring the particles cannot be specified from the shape,        the particle size is shown as an equivalent circle diameter. The        equivalent circle diameter is a value obtained by a circle        projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of each of the particlesis measured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetic average of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, and in a case of the definition (2), the average particle sizeis an average plate diameter. In a case of the definition (3), theaverage particle size is an average diameter (also referred to as anaverage particle diameter).

A content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50 to 90 mass % and more preferably 60 to90 mass %. A component other than the ferromagnetic powder of themagnetic layer is at least a binding agent, and one or more kinds ofadditives can be randomly included. A high filling percentage of theferromagnetic powder in the magnetic layer is preferable from aviewpoint of improvement of recording density.

Binding Agent and Curing Agent

The magnetic tape is a coating type magnetic tape and includes a bindingagent in the magnetic layer. The binding agent is one or more kinds ofresins. As the binding agent, various resins usually used as a bindingagent of a coating type magnetic recording medium can be used. Forexample, as the binding agent, a resin selected from a polyurethaneresin, a polyester resin, a polyamide resin, a vinyl chloride resin, anacrylic resin obtained by copolymerizing styrene, acrylonitrile, methylmethacrylate, or the like, a cellulose resin such as nitrocellulose, anepoxy resin, a phenoxy resin, and a polyvinylalkylal resin such aspolyvinyl acetal or polyvinyl butyral can be used alone or a pluralityof the resins can be mixed with each other to be used. Among these, apolyurethane resin, an acrylic resin, a cellulose resin, and a vinylchloride resin are preferable. These resins may be homopolymers orcopolymers. These resins can be used as the binding agent even in thenon-magnetic layer and/or a back coating layer which will be describedlater.

For the binding agent described above, descriptions disclosed inparagraphs 0028 to 0031 of JP2010-024113A can be referred to. An averagemolecular weight of the resin used as the binding agent can be, forexample, 10,000 or more and 200,000 or less as a weight-averagemolecular weight. The weight-average molecular weight of the presentinvention and this specification is a value obtained by performingpolystyrene conversion of a value measured under the followingmeasurement conditions by gel permeation chromatography (GPC). Theweight-average molecular weight of the binding agent shown in exampleswhich will be described later is a value obtained by performingpolystyrene conversion of a value measured under the followingmeasurement conditions.

-   -   GPC device: HLC-8120 (manufactured by Tosoh Corporation)    -   Column: TSK gel Multipore HXL-M (manufactured by Tosoh        Corporation, 7.8 mm ID (inner diameter)×30.0 cm)    -   Eluent: Tetrahydrofuran (THF)

In an aspect, as a binding agent, a binding agent containing an acidicgroup can be used. The acidic group in the present invention and thisspecification is used in a meaning including a form of a group capableof releasing H⁺ in water or a solvent including water (aqueous solvent)to be dissociated into an anion and a salt thereof. As a specificexample of an acidic group, a form of each of a sulfonic acid group, asulfuric acid group, a carboxy group, a phosphoric acid group, and asalt thereof, can be used, for example. For example, a form of a salt ofa sulfonic acid group (—SO₃H) means a group represented by —SO₃M, whereM represents a group representing an atom (for example, an alkali metalatom or the like) which can be a cation in water or an aqueous solvent.The same applies to the form of each of salts of the various groupsdescribed above. As an example of a binding agent containing an acidicgroup, a resin containing at least one type of acidic group selectedfrom the group consisting of a sulfonic acid group and a salt thereof(for example, a polyurethane resin, vinyl chloride resin, or the like)can be used, for example. Here, the resin included in the magnetic layeris not limited to these resins. In the binding agent containing anacidic group, an acidic group content can be, for example, in a range of0.03 to 0.50 meq/g. Contents of various functional groups such as anacidic group included in a resin, can be obtained by a well-known methodaccording to the kind of functional group. The binding agent can be usedin a magnetic layer forming composition in an amount of, for example,1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of theferromagnetic powder.

In regards to the controlling of the isoelectric point of the surfacezeta potential of the magnetic layer, it is supposed that formation ofthe magnetic layer so that an acid component is unevenly distributed ina surface layer part of the magnetic layer contributes to a decrease invalue of the isoelectric point. In addition, it is supposed thatformation of the magnetic layer to reduce the amount of a basiccomponent present in the surface layer part of the magnetic layer alsocontributes to a decrease in value of the isoelectric point. The acidcomponent is used in a meaning including a form of a component capableof releasing H⁺ in water or an aqueous solvent to be dissociated into ananion and a salt thereof. The basic component is used in a meaningincluding a form of a component capable of releasing OH⁻ in water or anaqueous solvent to be dissociated into a cation and a salt thereof. Forexample, it is considered that in a case where the acid component isused, uneven distribution of the acid component in the surface layerpart of the magnetic layer leads to a decrease in value of theisoelectric point of the surface zeta potential of the magnetic layer tocontrol the isoelectric point to be 3.8 or less. For example, it isconsidered that in a step of applying the magnetic layer formingcomposition onto a non-magnetic support directly or through anon-magnetic layer, the applying which is performed in an alternatingcurrent magnetic field by applying an alternating current magnetic fieldcontributes to formation of a magnetic layer in which the acid componentis unevenly distributed in the surface layer part. As the acidiccomponent, a binding agent containing an acidic group can be used, forexample. In addition, it is supposed that in a case where the bindingagent containing an acidic group is used, in a step of preparing themagnetic layer forming composition, the addition (additional addition)of the binding agent even in a case of preparing a dispersion liquid(magnetic liquid) containing ferromagnetic powder and the binding agentand then mixing the magnetic liquid with other components contributes toformation of a magnetic layer in which the binding agent containing theacidic group is unevenly distributed in the surface layer part. Detailsof the magnetic layer formation will be further described later.

In addition, a curing agent can also be used together with a resinusable as the binding agent. As the curing agent, in an aspect, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother aspect, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in a magnetic layerforming step. The same applies to the layer formed using thiscomposition in a case where the composition used to form the other layerincludes a curing agent. The preferred curing agent is a thermosettingcompound, and polyisocyanate is suitable for this. For details of thepolyisocyanate, descriptions disclosed in paragraphs 0124 and 0125 ofJP2011-216149A can be referred to. The curing agent can be used in themagnetic layer forming composition in an amount of, for example, 0 to80.0 parts by mass, and preferably 50.0 to 80.0 parts by mass, from aviewpoint of improvement of a strength of the magnetic layer, withrespect to 100.0 parts by mass of the binding agent.

Additive

The magnetic layer may include a ferromagnetic powder and a bindingagent, and, as necessary, include one or more kinds of additives. As theadditive, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include non-magnetic powder (for example, inorganic powder orcarbon black), a lubricant, a dispersing agent, a dispersing assistant,an antibacterial agent, an antistatic agent, and an antioxidant. As thenon-magnetic powder, non-magnetic powder which can function as anabrasive, or non-magnetic powder which can function as a protrusionforming agent which forms protrusions suitably protruded from themagnetic layer surface (for example, non-magnetic colloidal particles)is used. An average particle size of the colloidal silica (silicacolloidal particles) shown in examples which will be described later isa value obtained by a method disclosed in a paragraph 0015 ofJP2011-048878A as a measurement method of an average particle diameter.As the additive, a commercially available product can be suitablyselected or manufactured by a well-known method according to the desiredproperties, and any amount thereof can be used. As an example of theadditive which can be used in the magnetic layer including the abrasive,a dispersing agent disclosed in paragraphs 0012 to 0022 ofJP2013-131285A can be used as a dispersing agent for improvingdispersibility of the abrasive. For example, for the lubricant,descriptions disclosed in paragraphs 0030 to 0033, 0035, and 0036 ofJP2016-126817A can be referred to. The non-magnetic layer may include alubricant. For the lubricant which may be included in the non-magneticlayer, descriptions disclosed in paragraphs 0030, 0031, 0034, 0035, and0036 of JP2016-126817A can be referred to. For the dispersing agent,descriptions disclosed in paragraphs 0061 and 0071 of JP2012-133837A canbe referred to. The dispersing agent may be included in the non-magneticlayer. For the dispersing agent which can be included in thenon-magnetic layer, a description disclosed in a paragraph 0061 ofJP2012-133837A can be referred to.

The magnetic layer described above can be provided on the surface of thenon-magnetic support directly or indirectly through the non-magneticlayer.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer on a non-magnetic support directly, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substance or powder of organic substance. In addition, carbonblack and the like can be used. Examples of the inorganic substanceinclude metal, metal oxide, metal carbonate, metal sulfate, metalnitride, metal carbide, and metal sulfide. These non-magnetic powderscan be purchased as a commercially available product or can bemanufactured by a well-known method. For details thereof, descriptionsdisclosed in paragraphs 0146 to 0150 of JP2011-216149A can be referredto. For carbon black which can be used in the non-magnetic layer,descriptions disclosed in paragraphs 0040 and 0041 of JP2010-024113A canbe referred to. The content (filling percentage) of the non-magneticpowder of the non-magnetic layer is preferably 50 to 90 mass % and morepreferably 60 to 90 mass %.

In regards to other details of a binding agent or an additive of thenon-magnetic layer, the well-known technique regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technique regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities, for example, or intentionally,together with the non-magnetic powder. Here, the substantiallynon-magnetic layer is a layer having a residual magnetic flux density of10 mT or less, a layer having a coercivity of 7.96 kA/m (100 Oe) orless, or a layer having a residual magnetic flux density of 10 mT orless and a coercivity of 7.96 kA/m (100 Oe) or less. It is preferablethat the non-magnetic layer does not have a residual magnetic fluxdensity and a coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, and aromatic polyamidesubjected to biaxial stretching are used. Among these, polyethyleneterephthalate, polyethylene naphthalate, and polyamide are preferable.Corona discharge, plasma treatment, easy-bonding treatment, or thermaltreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape may or may not include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to the surface provided with the magneticlayer. Preferably, the back coating layer includes one or both of carbonblack and inorganic powder. In regards to the binding agent included inthe back coating layer and various additives which can be randomlyincluded in the back coating layer, the well-known technique regardingthe back coating layer can be applied, and the well-known techniqueregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied. For example, for the back coating layer,descriptions disclosed in paragraphs 0018 to 0020 of JP2006-331625A andpage 4, line 65, to page 5, line 38, of U.S. Pat. No. 7,029,774B can bereferred to.

Various Thicknesses

A thickness of the non-magnetic support is preferably 3.00 to 20.00 μm,more preferably 3.00 to 10.00 μm, and still more preferably 3.00 to 6.00μm.

A thickness of the magnetic layer can be optimized according to asaturation magnetization amount of the used magnetic head, a head gaplength, a band of a recording signal, and the like. A thickness of themagnetic layer is generally 0.01 μm to 0.15 μm, and preferably 0.02 μmto 0.12 μm and more preferably 0.03 μm to 0.10 μm from a viewpoint ofhigh density recording. The magnetic layer may be at least a singlelayer, the magnetic layer may be separated into two or more layershaving different magnetic properties, and a configuration of awell-known multilayered magnetic layer can be applied as the magneticlayer. A thickness of the magnetic layer in a case where the magneticlayer is separated into two or more layers is a total thickness of thelayers.

A thickness of the non-magnetic layer is, for example, 0.10 to 1.50 μmand is preferably 0.10 to 1.00 μm.

A thickness of the back coating layer is preferably 0.90 μm or less andmore preferably in the range of 0.10 to 0.70 μm.

The thickness of each layer of the magnetic tape and the non-magneticsupport can be obtained by a well-known film thickness measurementmethod. As an example, after a cross section of the magnetic tape in athickness direction is, for example, exposed by a well-known method ofion beams or microtome, and the exposed cross section is observed with ascanning electron microscope. In the cross section observation, variousthicknesses can be obtained as a thickness obtained at one portion, oran arithmetic average of thicknesses obtained at a plurality of portionsof two or more portions, for example, two portions which are randomlyextracted. In addition, the thickness of each layer may be obtained as adesigned thickness calculated according to the manufacturing conditions.

Method of Manufacturing Magnetic Tape

Manufacturing of Magnetic Tape Having Servo Pattern

A composition for forming the magnetic layer, the back coating layer,and the optionally provided non-magnetic layer usually contains asolvent together with the various components described above. As asolvent, various organic solvents generally used for manufacturing acoating type magnetic recording medium can be used. The amount of thesolvent in each layer forming composition is not particularly limited,and can be the same as that of each layer forming composition of atypical coating type magnetic recording medium. A step of preparing acomposition for forming each layer can usually include at least akneading step, a dispersing step, and a mixing step provided before andafter these steps, as necessary. Each step may be divided into two ormore stages. The component used in the preparation of each layer formingcomposition may be added at an initial stage or in a middle stage ofeach step. In addition, each component may be separately added in two ormore steps. For example, in the preparation of the magnetic layerforming composition, a binding agent containing an acidic group can beseparately added through two or more steps. It is preferable that thebinding agent containing an acidic group is added even in a step ofpreparing a dispersion liquid by mixing some components containing theferromagnetic powder among the various components of the magnetic layerforming composition with the binding agent containing an acidic groupand dispersing the mixture in a solvent, and mixing the dispersionliquid with the remaining components and performing dispersing, becauseit is possible to contribute to the controlling of the isoelectric pointof a surface zeta potential of the magnetic layer to be 3.8 or less. Inaddition, it is preferable that the non-magnetic powder which canfunction as an abrasive is dispersed separately from the ferromagneticpowder, and then mixed and dispersed with other components such as theferromagnetic powder, in order to improve dispersibility of theferromagnetic powder and the non-magnetic powder (abrasive).

In order to prepare each layer forming composition, a well-knowntechnique can be used. In the kneading step, preferably, a kneaderhaving a strong kneading force such as an open kneader, a continuouskneader, a pressure kneader, or an extruder is used. The details of thekneading processes of these kneaders are disclosed in JP1989-106338A(JP-H01-106338A) and JP1989-079274A (JP-H01-079274A). In addition, inorder to disperse each layer forming composition, one or more kinds ofdispersion beads selected from the group consisting of glass beads andother dispersion beads can be used as a dispersion medium. As suchdispersion beads, zirconia beads, titania beads, and steel beads whichare dispersion beads having high specific gravity are suitable. Thesedispersion beads can be used by optimizing a particle diameter (beaddiameter) and a filling percentage. As a dispersing device, a well-knowndispersing device can be used. Each layer forming composition may befiltered by a well-known method before performing the coating step. Thefiltering can be performed by using a filter, for example. As the filterused in the filtering, a filter having a pore diameter of 0.01 to 3 μm(for example, filter made of glass fiber or filter made ofpolypropylene) can be used, for example.

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support orperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying a back coatinglayer forming composition onto the surface of the non-magnetic supporton which the magnetic layer is formed or on the surface thereof on aside opposite to the surface on which the magnetic layer is to beformed. For details of the coating for forming each layer, a descriptiondisclosed in a paragraph 0066 of JP2010-231843A can be referred to.

The coating of the magnetic layer forming composition performed in analternating current magnetic field can contribute to the controlling ofthe isoelectric point of a surface zeta potential of the magnetic layerto be 3.8 or less. It is supposed that since an acidic component (forexample, a binding agent containing an acidic group) is easily unevenlydistributed in a surface portion of a coating layer of the magneticlayer forming composition due to the applied alternating currentmagnetic field, a magnetic layer in which the acidic component isunevenly distributed in the surface portion is obtained by drying thiscoating layer. The applying of the alternating current magnetic fieldcan be performed by disposing a magnet in a coating device so that thealternating current magnetic field is applied vertically to the surfaceof the coating layer of the magnetic layer forming composition. Amagnetic field intensity of the alternating current magnetic field canbe set to about 0.05 to 3.00 T, for example. However, there is nolimitation to this range.

The term “vertical” in the present invention and this specification doesnot necessarily mean only a vertical direction in strict meaning, butincludes a range of errors allowed in the technical field to which thepresent invention belongs. The range of errors can mean, for example, arange of less than ±10° from an exact vertical direction.

For details of various other steps for manufacturing the magnetic tape,the well-known technique can be applied. For various steps, descriptionsdisclosed in paragraphs 0067 to 0070 of JP2010-231843A can be referredto, for example. Preferably, the coating layer of the magnetic layerforming composition is subjected to an orientation process while thecoating layer is in a wet (not dried) state. For the orientationprocess, various well-known techniques such as a description disclosedin a paragraph 0067 of JP2010-231843A can be used. For example, avertical orientation process can be performed by a well-known methodsuch as a method using a polar opposing magnet. In an orientation zone,a drying speed of the coating layer can be controlled depending on atemperature and a flow rate of dry air and/or a transportation speed ofthe magnetic tape in the orientation zone. In addition, the coatinglayer may be preliminarily dried before the transportation to theorientation zone. In a case of performing the orientation process, it ispreferable to apply a magnetic field (for example, a direct currentmagnetic field) for orienting the ferromagnetic powder with respect tothe coating layer of the magnetic layer forming composition applied inan alternating current magnetic field.

Servo Pattern Formation

The magnetic tape has a timing-based servo pattern in the magneticlayer. FIG. 14 shows a disposition example of a region (servo band) inwhich the timing-based servo pattern is formed and a region (data band)which is interposed between two servo bands. FIG. 15 shows a dispositionexample of the timing-based servo pattern. Specific examples of a shapeof the timing-based servo pattern are shown in FIGS. 15 to 17 and FIGS.19 to 21. Here, the disposition example and/or the shape shown in eachdrawing is merely an example, and a servo pattern, a servo band, and adata band may be formed and disposed in a shape and a dispositionaccording to a type of the magnetic tape apparatus (drive). Further, fora shape and a disposition of the timing-based servo pattern, it ispossible to apply the well-known technique such as disposition examplesillustrated in, for example, FIG. 4, FIG. 5, FIG. 6, FIG. 9, FIG. 17,and FIG. 20 of U.S. Pat. No. 5,689,384A without any limitation.

The servo pattern can be formed by magnetizing a specific region of themagnetic layer with the servo write head mounted on a servo writer. Inthe timing-based servo system, for example, a servo signal is obtainedby reading pairs of non-parallel servo patterns (also referred to as“servo stripes”) continuously disposed in plural in a longitudinaldirection of a magnetic tape by a servo element.

In an aspect, as shown in JP2004-318983A, information indicating a servoband number (also referred to as “servo band ID (identification)” or“UDIM (Unique Data Band Identification Method) information”) is embeddedin each servo band. This servo band ID is recorded by shifting aspecific one of the plurality of pairs of the servo patterns in theservo band so that positions thereof are relatively displaced in alongitudinal direction of the magnetic tape. Specifically, a way ofshifting the specific one of the plurality of pairs of servo patterns ischanged for each servo band. Accordingly, the recorded servo band ID isunique for each servo band, and thus, the servo band can be uniquelyspecified only by reading one servo band with a servo element.

As a method for uniquely specifying a servo band, there is a methodusing a staggered method as shown in ECMA (European ComputerManufacturers Association)-319. In this staggered method, a group ofpairs of non-parallel servo patterns (servo stripes) disposedcontinuously in plural in a longitudinal direction of the magnetic tapeis recorded so as to be shifted in a longitudinal direction of themagnetic tape for each servo band. Since this combination of shiftingmethods between adjacent servo bands is unique throughout the magnetictape, it is possible to uniquely specify a servo band in a case ofreading a servo pattern with two servo elements.

As shown in ECMA-319, information indicating a position of the magnetictape in the longitudinal direction (also referred to as “LPOS(Longitudinal Position) information”) is usually embedded in each servoband. This LPOS information is also recorded by shifting the positionsof the pair of servo patterns in the longitudinal direction of themagnetic tape, as the UDIM information. Here, unlike the UDIMinformation, in this LPOS information, the same signal is recorded ineach servo band.

It is also possible to embed, in the servo band, the other informationdifferent from the above UDIM information and LPOS information. In thiscase, the embedded information may be different for each servo band asthe UDIM information or may be common to all servo bands as the LPOSinformation.

As a method of embedding information in the servo band, it is possibleto employ a method other than the above. For example, a predeterminedcode may be recorded by thinning out a predetermined pair from the groupof pairs of servo patterns.

The servo write head has a pair of gaps corresponding to the pair ofservo patterns as many as the number of servo bands. Usually, a core anda coil are connected to each pair of gaps, and by supplying a currentpulse to the coil, a magnetic field generated in the core can causegeneration of a leakage magnetic field in the pair of gaps. In a case offorming the servo pattern, by inputting a current pulse while runningthe magnetic tape on the servo write head, the magnetic patterncorresponding to the pair of gaps is transferred to the magnetic tape toform the servo pattern.

A width of each gap can be appropriately set according to a density ofthe servo pattern to be formed. The width of each gap can be set to, forexample, 1 μm or less, 1 to 10 μm, 10 μm or more, and the like.

Before the servo pattern is formed on the magnetic tape, the magnetictape is usually subjected to a demagnetization (erasing) process. Thiserasing process can be performed by applying a uniform magnetic field tothe magnetic tape using a direct current magnet or an alternatingcurrent magnet. The erasing process includes direct current (DC) erasingand alternating current (AC) erasing. AC erasing is performed bygradually decreasing an intensity of the magnetic field while reversinga direction of the magnetic field applied to the magnetic tape. On theother hand, DC erasing is performed by applying a unidirectionalmagnetic field to the magnetic tape. As the DC erasing, there are twomethods. A first method is horizontal DC erasing of applying a magneticfield in one direction along a longitudinal direction of the magnetictape. A second method is vertical DC erasing of applying a magneticfield in one direction along a thickness direction of the magnetic tape.The erasing process may be performed on the entire magnetic tape or maybe performed for each servo band of the magnetic tape.

A direction of the magnetic field of the servo pattern to be formed isdetermined according to a direction of the erasing. For example, in acase where the horizontal DC erasing is performed to the magnetic tape,the servo pattern is formed so that the direction of the magnetic fieldis opposite to the direction of the erasing. Therefore, an output of aservo signal obtained by reading the servo pattern can be increased. Asshown in JP2012-053940A, in a case where a pattern is transferred to,using the gap, a magnetic tape that has been subjected to vertical DCerasing, a servo signal obtained by reading the formed servo pattern hasa monopolar pulse shape. On the other hand, in a case where a pattern istransferred to, using the gap, a magnetic tape that has been subjectedto horizontal DC erasing, a servo signal obtained by reading the formedservo pattern has a bipolar pulse shape.

The magnetic tape described above is usually accommodated in a magnetictape cartridge and the magnetic tape cartridge is mounted in themagnetic tape apparatus.

Magnetic Tape Cartridge

An aspect of the present invention relates to a magnetic tape cartridgecomprising the above magnetic tape.

Details of the magnetic tape included in the magnetic tape cartridge areas described above.

In the magnetic tape cartridge, generally, the magnetic tape isaccommodated inside a cartridge body in a state of being wound around areel. The reel is rotatably provided inside the cartridge body. As themagnetic tape cartridge, a single reel type magnetic tape cartridgehaving one reel inside the cartridge body and a dual reel type magnetictape cartridge having two reels inside the cartridge body are widelyused. In a case where the single reel type magnetic tape cartridge ismounted on a magnetic tape apparatus (drive) for recording and/orreproducing information (magnetic signal) on the magnetic tape, themagnetic tape is pulled out of the magnetic tape cartridge to be woundaround the reel on the drive side. A magnetic head is disposed in amagnetic tape transportation path from the magnetic tape cartridge to awinding reel. Feeding and winding of the magnetic tape are performedbetween a reel (supply reel) on the magnetic tape cartridge side and areel (winding reel) on the drive side. During this time, information isrecorded and/or reproduced as the magnetic head and the magnetic layersurface of the magnetic tape come into contact with each other to beslid on each other. On the other hand, in the dual reel type magnetictape cartridge, both the supply reel and the winding reel are providedinside the magnetic tape cartridge. The magnetic tape cartridge may beeither a single reel type or a dual reel type magnetic tape cartridge.The magnetic tape cartridge has only to include the magnetic tapeaccording to the aspect of the present invention, and the well-knowntechnique can be applied to the others. For the aspect of the magnetictape cartridge, the above-mentioned description regarding the magnetictape cartridge 12 in FIG. 1 can be referred to.

Magnetic Tape Apparatus

An aspect of the present invention relates to a magnetic tape apparatusincluding the above described magnetic tape, a reading element unit, andan extraction unit, in which the reading element unit includes aplurality of reading elements each of which reads data from a specifictrack region including a reading target track in a track region includedin the magnetic tape, and in which the extraction unit performs awaveform equalization process with respect to each reading result foreach reading element, to extract, from the reading result, data derivedfrom the reading target track. Such a magnetic tape apparatus is asdescribed in detail above.

EXAMPLES

Hereinafter, the present invention will be described with reference toexamples. Here, the present invention is not limited to aspects shown inthe examples. Unless otherwise noted, “parts” and “%” described beloware based on mass. In addition, steps and evaluations described belowwere performed in an environment of an atmosphere temperature of 23°C.±1° C., unless otherwise noted. “eq” in the following description isan equivalent and is a unit that cannot be converted into SI unit.

A “binding agent A” described below is a SO₃Na group-containingpolyurethane resin (weight-average molecular weight: 70,000, SO₃Nagroup: 0.20 meq/g).

A “binding agent B” described below is a vinyl chloride copolymer(product name: MR110, SO₃K group-containing vinyl chloride copolymer,SO₃K group: 0.07 meq/g) manufactured by Kaneka Corporation.

An activation volume in Table 1 is a value obtained by the methoddescribed above for each ferromagnetic powder using a vibrating samplemagnetometer (manufactured by Toei Kogyo Co., Ltd.).

Manufacturing of Magnetic Tape

Example 1

(1) Preparation of Alumina Dispersion

3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 31.3 parts of a 32% solution (solvent is a mixedsolvent of methyl ethyl ketone and toluene) of a SO₃Na group-containingpolyester polyurethane resin (UR-4800 (SO₃Na group: 0.08 meq/g)manufactured by Toyobo Co., Ltd.), and 570.0 parts of a mixed solutionof methyl ethyl ketone and cyclohexanone (mass ratio of 1:1) as asolvent were mixed with respect to 100.0 parts of alumina powder (HIT-80manufactured by Sumitomo Chemical Co., Ltd) having a gelatinizationratio of about 65% and a brunauer-emmett-teller (BET) specific surfacearea of 20 m²/g, and this mixture was dispersed in the presence ofzirconia beads by a paint shaker for 5 hours. After the dispersion, thedispersion liquid and the beads were separated by a mesh and an aluminadispersion was obtained.

(2) Treatment of Magnetic Layer Forming Composition

Magnetic Liquid Ferromagnetic powder 100.0 parts Type: hexagonal bariumferrite powder, activation volume: see Table 1) Binding agent (type: seeTable 1) see Table 1 Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0parts Abrasive Liquid Alumina dispersion prepared above (1) 6.0 partsSilica Sol (Protrusion Forming Agent Liquid) Colloidal silica (averageparticle size: 120 nm) 2.0 parts Methyl ethyl ketone 1.4 parts OtherComponents Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butylstearate 2.0 parts Polyisocyanate (CORONATE (registered trademark) 2.5parts manufactured by Tosoh Corporation) Finishing Additive SolventCyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(3) Treatment of Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particlesize (average long axis length): 0.15 μm Average acicular ratio: 7 BETspecific surface area: 52 m²/g Carbon black 20.0 parts Average particlesize: 20 nm Binding agent A 18.0 parts Stearic acid 2.0 parts Stearicacid amide 0.2 parts Butyl stearate 2.0 parts Cyclohexanone 300.0 partsMethyl ethyl ketone 300.0 parts

(4) Treatment of Back Coating Layer Forming Composition

Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particlesize (average long axis length): 0.15 μm Average acicular ratio: 7 BETspecific surface area: 52 m²/g Carbon black 20.0 parts Average particlesize: 20 nm Vinyl chloride copolymer 13.0 parts Sulfonategroup-containing polyurethane resin 6.0 parts Phenylphosphonic acid 3.0parts Methyl ethyl ketone 155.0 parts Polyisocyanate 5.0 partsCyclohexanone 355.0 parts

(5) Preparation of Each Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

The magnetic liquid was prepared by dispersing (beads-dispersing) eachcomponent by using a batch type vertical sand mill for 24 hours. As thedispersion beads, zirconia beads having a bead diameter of 0.5 mm wereused.

The prepared magnetic liquid, the abrasive liquid, the binding agent Aadditionally added (0.1 parts with respect to 100.0 parts of theferromagnetic powder of the magnetic liquid), and other components(silica sol, other components, and finishing additive solvent) weremixed with one another and beads-dispersed for 5 minutes by using thesand mill, and the treatment (ultrasonic dispersion) was performed witha batch type ultrasonic device (20 kHz, 300 W) for 0.5 minutes.Thereafter, the resultant dispersion liquid was filtered using a filterhaving a pore diameter of 0.5 μm, and the magnetic layer formingcomposition was prepared.

The non-magnetic layer forming composition was prepared by the followingmethod.

Each component excluding a lubricant (stearic acid, stearic acid amide,and butyl stearate), cyclohexanone, and methyl ethyl ketone wasdispersed by using a batch type vertical sand mill for 24 hours toobtain a dispersion liquid. As the dispersion beads, zirconia beadshaving a bead diameter of 0.5 mm were used. Thereafter, the remainingcomponents were added into the obtained dispersion liquid and werestirred by a dissolver. The dispersion liquid obtained as describedabove was filtered using a filter having a pore diameter of 0.5 μm, andthus a non-magnetic layer forming composition was prepared.

The back coating layer forming composition was prepared by the followingmethod.

Each component excluding polyisocyanate and cyclohexanone was kneadedand diluted by an open kneader, and was subjected to dispersionprocesses of 12 passes, with a horizontal beads mill disperser usingzirconia beads having a bead diameter of 1 mm, by setting a retentiontime per pass to 2 minutes at a bead filling rate of 80 vol % and arotor tip circumferential speed of 10 msec. Thereafter, the remainingcomponents were added into the obtained dispersion liquid and werestirred by a dissolver. The dispersion liquid obtained as describedabove was filtered using a filter having a pore diameter of 1 μm, andthus a back coating layer forming composition was prepared.

(6) Method of Manufacturing Magnetic Tape

The non-magnetic layer forming composition prepared in the section (5)was applied onto a surface of a support made of biaxially stretchedpolyethylene naphthalate having a thickness of 5.00 μm so that thethickness after the drying becomes 1.00 μm and was dried to form anon-magnetic layer.

Then, in a coating device disposed with a magnet for applying analternating current magnetic field, the magnetic layer formingcomposition prepared in the section (5) was applied onto a surface of anon-magnetic layer so that the thickness after the drying becomes 0.10μm, while applying an alternating current magnetic field (magnetic fieldintensity: 0.15 T) to form a coating layer. The applying of thealternating current magnetic field was performed so that the alternatingcurrent magnetic field was applied vertically to the surface of thecoating layer. After that, a vertical orientation process was performedby applying a direct current magnetic field having a magnetic fieldintensity of 0.30 T in a vertical direction with respect to a surface ofa coating layer, while the coating layer of the magnetic layer formingcomposition is in a wet (not dried) state. After that, the coating layerwas dried to form a magnetic layer.

After that, the back coating layer forming composition prepared in thesection (5) was applied onto the surface of the support made ofpolyethylene naphthalate on a side opposite to the surface on which thenon-magnetic layer and the magnetic layer were formed, so that thethickness after the drying becomes 0.50 μm, and was dried to form a backcoating layer.

After that, a surface smoothing treatment (calendering treatment) wasperformed using a calender roll configured of only a metal roll, at aspeed of 100 m/min, a linear pressure of 294 kN/m (300 kg/cm), and acalender temperature (surface temperature of a calender roll) of 100° C.

Then, the thermal treatment was performed in an environment of anatmosphere temperature of 70° C. for 36 hours. After the thermaltreatment, slitting was performed to have a width of ½ inches (0.0127meters) to obtain a magnetic tape.

In a state where the magnetic layer of the obtained magnetic tape wasdemagnetized, a servo pattern (timing-based servo pattern) having adisposition and a shape according to an LTO Ultrium format was formed onthe magnetic layer by a servo write head (leakage magnetic field: 247kA/m) mounted on the servo writer. Accordingly, a magnetic tape ofExample 1 including data bands, servo bands, and guide bands in thedisposition according to the LTO Ultrium format in the magnetic layer,and including servo patterns having the disposition and the shapeaccording to the LTO Ultrium format on the servo band was obtained.

Examples 2 to 6 and Comparative Examples 1 to 8

A magnetic tape was manufactured by the same manner as in Example 1except that various conditions were changed as shown in Table 1.

In Table 1, in the examples and the comparative examples in which“Performed” is disclosed in the column of the additional addition of thebinding agent, the additional addition of the binding agent A (0.1 partswith respect to 100.0 parts of the ferromagnetic powder of the magneticliquid) was performed in the same manner as in Example 1. On the otherhand, in the comparative examples in which “Not performed” is shown inthis column, the additional addition of the binding agent was notperformed.

In Table 1, in the examples and the comparative examples in which“Performed” is shown in the column of the alternating current magneticfield application during coating, the steps subsequent to the coatingstep of the magnetic layer forming composition were performed by thesame manner as in Example 1. That is, the application of the alternatingcurrent magnetic field was applied during coating of the magnetic layerforming composition in the same manner as in Example 1. On the otherhand, in the comparative examples in which “Not performed” is shown inthis column, the steps subsequent to the coating step of the magneticlayer forming composition were performed by the same manner as inExample 1, except that the application of the alternating currentmagnetic field was not applied.

Comparative Example 9

A magnetic tape was manufactured in the same manner as in Example 1except that hexagonal barium ferrite powder having an activation volumeshown in Table 1 was used as ferromagnetic powder, various conditionswere changed as shown in Table 1, and a servo write head having aleakage magnetic field of 366 kA/m was used as the servo write head.

Evaluation of Physical Properties

(1) Isoelectric Point of Surface Zeta Potential of Magnetic Layer

Six samples for isoelectric point measurement were cut out from eachmagnetic tape of the examples and the comparative examples, and twosamples were disposed in a measurement cell in one measurement. In themeasurement cell, a sample installing surface and a surface of the backcoating layer of the sample were bonded to each other by using adouble-sided tape in an upper and lower sample table (size of eachsample installing surface is 1 cm×2 cm) of the measurement cell. In acase where an electrolyte flows in the measurement cell after disposingthe two samples as described above, the magnetic layer surface of thetwo samples bonded to each other on the upper and lower sample table ofthe measurement cell comes into contact with the electrolyte, and thus,the surface zeta potential of the magnetic layer can be measured. Themeasurement was performed three times in total by using two samples ineach measurement, and the isoelectric points of the surface zetapotential of the magnetic layer were obtained. Table 1 shows anarithmetic average of the three values obtained by three times of themeasurement as the isoelectric point of the surface zeta potential ofthe magnetic layer of each magnetic tape. As a surface zeta potentialmeasurement device, SurPASS manufactured by Anton Paar was used. Themeasurement conditions were set as follows. Other details of the methodof obtaining the isoelectric point are as described above.

-   -   Measurement cell: variable gap cell (20 mm×10 mm)    -   Measurement mode: streaming current    -   Gap: about 200 μm    -   Measurement temperature: room temperature    -   Ramp target pressure/time: 400,000 Pa (400 mbar)/60 seconds    -   Electrolyte: KCl aqueous solution having concentration of 1        mmol/L (adjusted pH to 9)    -   pH adjusting solution: HCl aqueous solution having concentration        of 0.1 mol/L or KOH aqueous solution having concentration of 0.1        mol/L    -   Measurement pH: pH 9→pH 3 (measured at 13 measurement points in        total at interval of about 0.5)

(2) Difference (L_(99.9)−L_(0.1))

A difference (L_(99.9)−L_(0.1)) was obtained for each magnetic tape ofthe examples and the comparative examples by the following method.

Using Dimension 3100 manufactured by Bruker as a magnetic forcemicroscope in a frequency modulation mode and SSS-MFMR (nominalcurvature radius of 15 nm) manufactured by Nanoworld AG as a probe, in arange of 90 μm×90 μm of the magnetic layer surface of the magnetic tapeon which the servo pattern was formed, rough measurement was performedat a pitch of 100 nm to extract a servo pattern (magnetization region).A distance between a magnetic layer surface and a probe distal endduring magnetic force microscopy was 20 nm. Since the above measurementrange includes the five servo patterns of the A burst formed inaccordance with the LTO Ultrium format, these five servo patterns wereextracted.

The magnetic profile was obtained by measuring the vicinity of theboundary between the magnetization region and the non-magnetizationregion at a pitch of 5 nm, using the magnetic force microscope and theprobe, in a downstream edge of each servo pattern in a runningdirection. Since the obtained magnetic profile was inclined at an angleα=12°, rotation correction was performed by analysis software so thatthe angle α=0°.

The measurement was performed at three different portions on themagnetic layer surface. Each measurement range includes five servopatterns of the A burst.

Thereafter, the difference (L_(99.9)−L_(0.1)) was obtained by the methoddescribed above using analysis software. As analysis software, MATLABmanufactured by MathWorks was used. Such an obtained difference(L_(99.9)−L_(0.1)) is shown in Table 1.

Performance Evaluation

(1) The recording of data was performed on the magnetic layer of eachmagnetic tape of the examples and the comparative examples by using arecording and reproducing head mounted on TS1155 tape drive manufacturedby IBM Corporation, under recording conditions of a rate of 6 m/s, alinear recording density of 600 kbpi (255 bit PRBS), and a track pitchof 2 μm. The unit kbpi is a unit of linear recording density (cannot beconverted into SI unit system). The PRBS is an abbreviation of PseudoRandom Bit Sequence.

By the recording, a specific track region, where the reading targettrack is positioned, is formed on the magnetic layer of each magnetictape between two adjacent tracks, that is, between a first noise mixingsource track and a second noise mixing source track.

(2) The following data reading was performed as a model experiment ofperforming the data reading using the reading element unit including tworeading elements disposed in an adjacent state. In the following modelexperiment, the data reading was performed by bringing the magneticlayer surface and the reading element into contact with each other to beslid on each other.

The reading was started in a state where the magnetic head including asingle reading element was disposed so that the center of the readingtarget track in the tape width direction coincides with the center ofthe reading element in the track width direction, and a first datareading was performed. During this first data reading, the servo patternwas read by the servo element, and the tracking in the timing-basedservo system was also performed. In addition, the data reading operationwas performed by the reading element synchronously with the servopattern reading operation.

Then, the position of the same magnetic head was deviated in the tapewidth direction (one adjacent track side) by 500 nm, and a second datareading was performed, in the same manner as in the first data reading.The two times of data reading described above were respectivelyperformed under reading conditions of a reproducing element width of 0.2μm, a rate of 4 m/s, and a sampling rate:bit rate of 1.25 times.

A reading signal obtained by the first data reading was input to anequalizer, and the waveform equalization process according to thedeviation amount of the positions between the magnetic tape and themagnetic head (reading element) of the first data reading was performed.This waveform equalization process is a process performed as follows. Aratio between an overlapping region of the reading element and thereading target track and an overlapping region of the reading elementand the adjacent track is specified from the deviation amount of theposition obtained by reading the servo pattern formed at regular cycleby the servo element. A convolution arithmetic operation of a tapcoefficient derived from this specific ratio using an arithmeticexpression, was performed with respect to the reading signal, andaccordingly, the waveform equalization process was performed. Thearithmetic expression is an arithmetic expression in which ExtendedPartial Response class 4 (EPR4) is set as a reference waveform (target).Regarding a reading signal obtained in the second data reading, thewaveform equalization process was performed in the same manner.

By performing a phase matching process (two-dimensional signal process)of the two reading signals subjected to the waveform equalizationprocess, a reading signal which was expected to be obtained by thereading element unit including two reading elements disposed in anadjacent state (reading element pitch=500 nm) was obtained. Regardingthe reading signal obtained by doing so, an SNR at a signal detectionpoint was calculated.

(3) The operation of (2) was repeated while performing track off-set ofthe position of the reading element at the start of the first datareading to the first noise mixing source track and the second noisemixing source track, respectively from the center of the reading targettrack in the tape width direction at interval of 0.1 μm, and an envelopeof the SNR with respect to the track position was obtained.

In each of the examples and the comparative examples, the envelope ofthe SNR was obtained reading only the first data reading result (thatis, data reading result obtained with only a single element).

(4) The envelope of the SNR obtained regarding the data reading resultobtained with only the single element was set as a reference envelope,and the SNR decreased from the SNR of the track center of the referenceenvelope by −3 dB was set as an SNR lower limit value. Regarding eachenvelope, the maximum track off-set amount equal to or greater than thelower limit value was set as an allowable track off-set amount. Inrespective examples and the comparative examples, a rate of increase ofthe allowable track off-set amount with respect to the allowable trackoff-set amount obtained with only the single element was obtained as a“rate of increase of the allowable track off-set amount”.

The results described above are shown in Table 1 (Tables 1-1 and 1-2).

TABLE 1-1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Ferromagnetic Activation 1,600 nm³ 1,600 nm³ 1,600 nm³ 1,600 nm³ 1,600nm³ 1,600 nm³ powder volume Binding agent Binding 5.0 parts 10.0 parts15.0 parts 20.0 parts 0 parts 10.0 parts content of agent A magneticliquid Binding 0 parts 0 parts 0 parts 0 parts 10 parts 10 parts agent BAdditional addition Performed Performed Performed Performed PerformedPerformed of binding agent Application of Performed Performed PerformedPerformed Performed Performed alternating current magnetic field duringcoating Isoelectric point of 3.8 3.6 3.2 2.7 3.5 3.0 surface zetapotential of magnetic layer Difference (L_(99.9) − L_(0.1)) (nm) 180 180150 130 150 140 Rate of increase of 25 30 32 35 30 33 allowable trackoff-set amount (%)

Comparative Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Example 5 Ferromagnetic Activation 1,600nm³ 1,600 nm³ 1,600 nm³ 1,600 nm³ 1,600 nm³ powder volume Binding agentBinding 5.0 parts 10.0 parts 15.0 parts 20.0 parts 15.0 parts content ofagent A magnetic liquid Binding 0 parts 0 parts 0 parts 0 parts 0 partsagent B Additional addition Not performed Not performed Not performedNot performed Performed of binding agent Application of Not Notperformed Not performed Not performed Not performed alternating currentperformed magnetic field during coating Isoelectric point of 5.0 4.8 4.64.6 4.2 surface zeta potential of magnetic layer Difference (L_(99.9) −L_(0.1)) (nm) 260 260 255 260 260 Rate of increase of 2 2 3 2 2allowable track off-set amount (%) Comparative Comparative ComparativeComparative Example 6 Example 7 Example 8 Example 9 FerromagneticActivation 1,600 nm³ 1,600 nm³ 1,600 nm³ 2,500 nm³ powder volume Bindingagent Binding 15.0 parts 0 parts 10.0 parts 15.0 parts content of agentA magnetic liquid Binding 0 parts 10 parts 10 parts 0 parts agent BAdditional addition Not performed Not performed Not performed Notperformed of binding agent Application of Performed Not performed Notperformed Not performed alternating current magnetic field duringcoating Isoelectric point of 4.6 4.8 4.7 4.6 surface zeta potential ofmagnetic layer Difference (L_(99.9) − L_(0.1)) (nm) 260 260 260 155 Rateof increase of 2 2 2 15 allowable track off-set amount (%)

As shown in Table 1, according to the examples, the rate of increase ofthe allowable track off-set amount equal to or greater than 20% could berealized.

A large allowable track off-set amount obtained by the method describedabove is advantageous, from a viewpoint of performing the reproducingwith excellent reproducing quality, even with a small track margin. Fromthis viewpoint, a rate of increase of the allowable track off-set amountis preferably equal to or greater than 20%.

An aspect of the present invention is useful in magnetic recording whereit is desired to reproduce high density recorded data with excellentreproducing quality.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer including ferromagnetic powder and abinding agent, wherein the magnetic layer has a timing-based servopattern, wherein an edge shape of the timing-based servo pattern,specified by magnetic force microscopy is a shape in which a differenceL_(99.9)−L_(0.1) between a value L_(99.9) of a cumulative distributionfunction of 99.9% and a value L_(0.1) of a cumulative distributionfunction of 0.1% in a position deviation width from an ideal shape ofthe magnetic tape in a longitudinal direction is 180 nm or less, andwherein an isoelectric point of a surface zeta potential of the magneticlayer is 3.8 or less.
 2. The magnetic tape according to claim 1, whereinthe isoelectric point is 2.5 or more and 3.8 or less.
 3. The magnetictape according to claim 1, wherein the binding agent is a binding agentcontaining an acidic group.
 4. The magnetic tape according to claim 3,wherein the acidic group includes at least one type of acidic groupselected from the group consisting of a sulfonic acid group and a saltthereof.
 5. The magnetic tape according to claim 1, wherein thetiming-based servo pattern is a linear servo pattern which continuouslyextends from one side of the magnetic tape in a width direction to theother side thereof and is inclined at an angle α with respect to thewidth direction, and wherein the ideal shape is a linear shape extendingin a direction of the angle α.
 6. The magnetic tape according to claim1, wherein the difference L_(99.9)−L_(0.1) is 100 nm or more and 180 nmor less.
 7. The magnetic tape according to claim 1, further comprising:a non-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.
 8. The magnetictape according to claim 1, further comprising: a back coating layerincluding non-magnetic powder and a binding agent on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.
 9. A magnetic tape cartridge comprising: the magnetictape according to claim
 1. 10. The magnetic tape cartridge according toclaim 9, wherein the isoelectric point is 2.5 or more and 3.8 or less.11. The magnetic tape cartridge according to claim 9, wherein thebinding agent is a binding agent containing an acidic group.
 12. Themagnetic tape cartridge according to claim 11, wherein the acidic groupincludes at least one type of acidic group selected from the groupconsisting of a sulfonic acid group and a salt thereof.
 13. The magnetictape cartridge according to claim 9, wherein the timing-based servopattern is a linear servo pattern which continuously extends from oneside of the magnetic tape in a width direction to the other side thereofand is inclined at an angle α with respect to the width direction, andwherein the ideal shape is a linear shape extending in a direction ofthe angle α.
 14. The magnetic tape cartridge according to claim 9,wherein the difference L_(99.9)−L_(0.1) is 100 nm or more and 180 nm orless.
 15. A magnetic tape apparatus comprising: a magnetic tape; areading element unit; and an extraction unit, wherein the magnetic tapeis the magnetic tape according to claim 1, wherein the reading elementunit includes a plurality of reading elements each of which reads datafrom a specific track region including a reading target track in a trackregion included in the magnetic tape, and wherein the extraction unitperforms a waveform equalization process with respect to each readingresult for each reading element, to extract, from the reading result,data derived from the reading target track.
 16. The magnetic tapeapparatus according to claim 15, wherein the isoelectric point is 2.5 ormore and 3.8 or less.
 17. The magnetic tape apparatus according to claim15, wherein the binding agent is a binding agent containing an acidicgroup.
 18. The magnetic tape apparatus according to claim 17, whereinthe acidic group includes at least one type of acidic group selectedfrom the group consisting of a sulfonic acid group and a salt thereof.19. The magnetic tape apparatus according to claim 15, wherein thetiming-based servo pattern is a linear servo pattern which continuouslyextends from one side of the magnetic tape in a width direction to theother side thereof and is inclined at an angle α with respect to thewidth direction, and wherein the ideal shape is a linear shape extendingin a direction of the angle α.
 20. The magnetic tape apparatus accordingto claim 15, wherein the difference L_(99.9)−L_(0.1) is 100 nm or moreand 180 nm or less.